diff --git a/backend/app/api/tasks.py b/backend/app/api/tasks.py
index 904e1c3..98565d8 100644
--- a/backend/app/api/tasks.py
+++ b/backend/app/api/tasks.py
@@ -68,6 +68,7 @@ def _task_to_response(task: Task) -> TaskResponse:
             id=task.project.id,
             name=task.project.name,
             brand_name=task.project.brand.name if task.project.brand else None,
+            platform=task.project.platform,
         ),
         agency=AgencyInfo(
             id=task.agency.id,
diff --git a/backend/app/schemas/task.py b/backend/app/schemas/task.py
index 797e39e..95e20ea 100644
--- a/backend/app/schemas/task.py
+++ b/backend/app/schemas/task.py
@@ -87,6 +87,7 @@ class ProjectInfo(BaseModel):
     id: str
     name: str
     brand_name: Optional[str] = None
+    platform: Optional[str] = None
 
 
 class TaskResponse(BaseModel):
diff --git a/frontend/app/agency/appeals/page.tsx b/frontend/app/agency/appeals/page.tsx
index 02edb2e..c22af79 100644
--- a/frontend/app/agency/appeals/page.tsx
+++ b/frontend/app/agency/appeals/page.tsx
@@ -149,7 +149,7 @@ function mapTaskToAppeal(task: TaskResponse): Appeal {
     taskTitle: task.name,
     creatorId: task.creator.id,
     creatorName: task.creator.name,
-    platform: 'douyin', // Backend does not expose platform on task; default for now
+    platform: task.project?.platform || 'douyin',
     type,
     contentType,
     reason: task.appeal_reason || '申诉',
diff --git a/frontend/app/agency/briefs/[id]/page.tsx b/frontend/app/agency/briefs/[id]/page.tsx
index e0383db..e25659c 100644
--- a/frontend/app/agency/briefs/[id]/page.tsx
+++ b/frontend/app/agency/briefs/[id]/page.tsx
@@ -356,7 +356,7 @@ export default function BriefConfigPage() {
         id: brief?.id || `no-brief-${projectId}`,
         projectName: project.name,
         brandName: project.brand_name || '未知品牌',
-        platform: 'douyin', // 后端暂无 platform 字段
+        platform: project.platform || 'douyin',
         files: briefFiles,
         brandRules: {
           restrictions: brief?.other_requirements || '暂无限制条件',
@@ -418,15 +418,37 @@ export default function BriefConfigPage() {
     }
     try {
       const signedUrl = await api.getSignedUrl(file.url)
-      window.open(signedUrl, '_blank')
+      // 使用 a 标签触发下载
+      const a = document.createElement('a')
+      a.href = signedUrl
+      a.target = '_blank'
+      a.rel = 'noopener noreferrer'
+      a.download = file.name
+      document.body.appendChild(a)
+      a.click()
+      document.body.removeChild(a)
     } catch {
       toast.error('获取下载链接失败')
     }
   }
 
   // 预览文件
-  const handlePreview = (file: BriefFile) => {
+  const [previewUrl, setPreviewUrl] = useState<string | null>(null)
+  const [previewLoading, setPreviewLoading] = useState(false)
+  const handlePreview = async (file: BriefFile) => {
     setPreviewFile(file)
+    setPreviewUrl(null)
+    if (!USE_MOCK && file.url) {
+      setPreviewLoading(true)
+      try {
+        const signedUrl = await api.getSignedUrl(file.url)
+        setPreviewUrl(signedUrl)
+      } catch {
+        toast.error('获取预览链接失败')
+      } finally {
+        setPreviewLoading(false)
+      }
+    }
   }
 
   // 导出平台规则文档
@@ -622,8 +644,22 @@ export default function BriefConfigPage() {
     }))
   }
 
-  const handlePreviewAgencyFile = (file: AgencyFile) => {
+  const [previewAgencyUrl, setPreviewAgencyUrl] = useState<string | null>(null)
+  const [previewAgencyLoading, setPreviewAgencyLoading] = useState(false)
+  const handlePreviewAgencyFile = async (file: AgencyFile) => {
     setPreviewAgencyFile(file)
+    setPreviewAgencyUrl(null)
+    if (!USE_MOCK && file.url) {
+      setPreviewAgencyLoading(true)
+      try {
+        const signedUrl = await api.getSignedUrl(file.url)
+        setPreviewAgencyUrl(signedUrl)
+      } catch {
+        toast.error('获取预览链接失败')
+      } finally {
+        setPreviewAgencyLoading(false)
+      }
+    }
   }
 
   const handleDownloadAgencyFile = async (file: AgencyFile) => {
@@ -633,7 +669,14 @@ export default function BriefConfigPage() {
     }
     try {
       const signedUrl = await api.getSignedUrl(file.url)
-      window.open(signedUrl, '_blank')
+      const a = document.createElement('a')
+      a.href = signedUrl
+      a.target = '_blank'
+      a.rel = 'noopener noreferrer'
+      a.download = file.name
+      document.body.appendChild(a)
+      a.click()
+      document.body.removeChild(a)
     } catch {
       toast.error('获取下载链接失败')
     }
@@ -1179,20 +1222,44 @@ export default function BriefConfigPage() {
       {/* 文件预览弹窗（品牌方） */}
       <Modal
         isOpen={!!previewFile}
-        onClose={() => setPreviewFile(null)}
+        onClose={() => { setPreviewFile(null); setPreviewUrl(null) }}
         title={previewFile?.name || '文件预览'}
         size="lg"
       >
         <div className="space-y-4">
-          <div className="aspect-[4/3] bg-bg-elevated rounded-lg flex items-center justify-center">
-            <div className="text-center">
-              <FileText size={48} className="mx-auto text-text-tertiary mb-4" />
-              <p className="text-text-secondary">文件预览区域</p>
-              <p className="text-xs text-text-tertiary mt-1">实际开发中将嵌入文件预览组件</p>
-            </div>
+          <div className="bg-bg-elevated rounded-lg overflow-hidden" style={{ minHeight: '400px' }}>
+            {previewLoading ? (
+              <div className="flex items-center justify-center h-[400px]">
+                <Loader2 className="animate-spin text-accent-indigo" size={32} />
+                <span className="ml-2 text-text-secondary">加载预览中...</span>
+              </div>
+            ) : previewUrl && previewFile?.name.toLowerCase().endsWith('.pdf') ? (
+              <iframe
+                src={previewUrl}
+                className="w-full border-0 rounded-lg"
+                style={{ height: '500px' }}
+                title={previewFile?.name}
+              />
+            ) : previewUrl && /\.(jpg|jpeg|png|gif|webp)$/i.test(previewFile?.name || '') ? (
+              <div className="flex items-center justify-center p-4">
+                {/* eslint-disable-next-line @next/next/no-img-element */}
+                <img src={previewUrl} alt={previewFile?.name} className="max-w-full max-h-[500px] object-contain rounded" />
+              </div>
+            ) : previewUrl ? (
+              <div className="flex flex-col items-center justify-center h-[400px] text-center">
+                <FileText size={48} className="text-text-tertiary mb-4" />
+                <p className="text-text-secondary mb-1">该文件类型不支持在线预览</p>
+                <p className="text-xs text-text-tertiary">请下载后使用本地应用打开</p>
+              </div>
+            ) : (
+              <div className="flex flex-col items-center justify-center h-[400px] text-center">
+                <FileText size={48} className="text-text-tertiary mb-4" />
+                <p className="text-text-secondary">暂无预览链接</p>
+              </div>
+            )}
           </div>
           <div className="flex justify-end gap-2">
-            <Button variant="secondary" onClick={() => setPreviewFile(null)}>
+            <Button variant="secondary" onClick={() => { setPreviewFile(null); setPreviewUrl(null) }}>
               关闭
             </Button>
             {previewFile && (
@@ -1267,20 +1334,44 @@ export default function BriefConfigPage() {
       {/* 代理商文档预览弹窗 */}
       <Modal
         isOpen={!!previewAgencyFile}
-        onClose={() => setPreviewAgencyFile(null)}
+        onClose={() => { setPreviewAgencyFile(null); setPreviewAgencyUrl(null) }}
         title={previewAgencyFile?.name || '文件预览'}
         size="lg"
       >
         <div className="space-y-4">
-          <div className="aspect-[4/3] bg-bg-elevated rounded-lg flex items-center justify-center">
-            <div className="text-center">
-              <FileText size={48} className="mx-auto text-accent-indigo mb-4" />
-              <p className="text-text-secondary">文件预览区域</p>
-              <p className="text-xs text-text-tertiary mt-1">实际开发中将嵌入文件预览组件</p>
-            </div>
+          <div className="bg-bg-elevated rounded-lg overflow-hidden" style={{ minHeight: '400px' }}>
+            {previewAgencyLoading ? (
+              <div className="flex items-center justify-center h-[400px]">
+                <Loader2 className="animate-spin text-accent-indigo" size={32} />
+                <span className="ml-2 text-text-secondary">加载预览中...</span>
+              </div>
+            ) : previewAgencyUrl && previewAgencyFile?.name.toLowerCase().endsWith('.pdf') ? (
+              <iframe
+                src={previewAgencyUrl}
+                className="w-full border-0 rounded-lg"
+                style={{ height: '500px' }}
+                title={previewAgencyFile?.name}
+              />
+            ) : previewAgencyUrl && /\.(jpg|jpeg|png|gif|webp)$/i.test(previewAgencyFile?.name || '') ? (
+              <div className="flex items-center justify-center p-4">
+                {/* eslint-disable-next-line @next/next/no-img-element */}
+                <img src={previewAgencyUrl} alt={previewAgencyFile?.name} className="max-w-full max-h-[500px] object-contain rounded" />
+              </div>
+            ) : previewAgencyUrl ? (
+              <div className="flex flex-col items-center justify-center h-[400px] text-center">
+                <FileText size={48} className="text-text-tertiary mb-4" />
+                <p className="text-text-secondary mb-1">该文件类型不支持在线预览</p>
+                <p className="text-xs text-text-tertiary">请下载后使用本地应用打开</p>
+              </div>
+            ) : (
+              <div className="flex flex-col items-center justify-center h-[400px] text-center">
+                <FileText size={48} className="text-text-tertiary mb-4" />
+                <p className="text-text-secondary">暂无预览链接</p>
+              </div>
+            )}
           </div>
           <div className="flex justify-end gap-2">
-            <Button variant="secondary" onClick={() => setPreviewAgencyFile(null)}>
+            <Button variant="secondary" onClick={() => { setPreviewAgencyFile(null); setPreviewAgencyUrl(null) }}>
               关闭
             </Button>
             {previewAgencyFile && (
diff --git a/frontend/app/agency/briefs/page.tsx b/frontend/app/agency/briefs/page.tsx
index caef115..e48d9cf 100644
--- a/frontend/app/agency/briefs/page.tsx
+++ b/frontend/app/agency/briefs/page.tsx
@@ -141,7 +141,7 @@ export default function AgencyBriefsPage() {
               projectId: project.id,
               projectName: project.name,
               brandName: project.brand_name || '未知品牌',
-              platform: 'douyin', // 后端暂无 platform 字段，默认值
+              platform: project.platform || 'douyin',
               status: hasBrief ? 'configured' : 'pending',
               uploadedAt: project.created_at.split('T')[0],
               configuredAt: hasBrief ? brief.updated_at.split('T')[0] : null,
@@ -156,7 +156,7 @@ export default function AgencyBriefsPage() {
               projectId: project.id,
               projectName: project.name,
               brandName: project.brand_name || '未知品牌',
-              platform: 'douyin',
+              platform: project.platform || 'douyin',
               status: 'pending',
               uploadedAt: project.created_at.split('T')[0],
               configuredAt: null,
diff --git a/frontend/app/agency/creators/page.tsx b/frontend/app/agency/creators/page.tsx
index fc98883..6b27b7c 100644
--- a/frontend/app/agency/creators/page.tsx
+++ b/frontend/app/agency/creators/page.tsx
@@ -245,7 +245,7 @@ export default function AgencyCreatorsPage() {
       id: task.id,
       name: task.name,
       projectName: task.project?.name || '-',
-      platform: 'douyin', // 后端暂未返回平台信息，默认
+      platform: task.project?.platform || 'douyin',
       stage: mapBackendStage(task.stage),
       appealRemaining: task.appeal_count,
       appealUsed: task.is_appeal ? 1 : 0,
diff --git a/frontend/app/agency/tasks/[id]/page.tsx b/frontend/app/agency/tasks/[id]/page.tsx
index 8f6d563..2cb6a9c 100644
--- a/frontend/app/agency/tasks/[id]/page.tsx
+++ b/frontend/app/agency/tasks/[id]/page.tsx
@@ -8,8 +8,13 @@ import { Button } from '@/components/ui/Button'
 import { SuccessTag, WarningTag, ErrorTag, PendingTag } from '@/components/ui/Tag'
 import { api } from '@/lib/api'
 import { USE_MOCK } from '@/contexts/AuthContext'
+import { getPlatformInfo } from '@/lib/platforms'
 import type { TaskResponse, TaskStage } from '@/types/task'
 
+function getPlatformLabel(platformId: string): string {
+  return getPlatformInfo(platformId)?.name || platformId
+}
+
 // ==================== 本地视图模型 ====================
 interface TaskViewModel {
   id: string
@@ -225,7 +230,7 @@ function mapTaskResponseToViewModel(task: TaskResponse): TaskViewModel {
     videoTitle: task.name,
     creatorName: task.creator?.name || '未知达人',
     brandName: task.project?.brand_name || '未知品牌',
-    platform: '小红书', // 后端暂无 platform 字段
+    platform: task.project?.platform ? getPlatformLabel(task.project.platform) : '未知平台',
     status,
     aiScore,
     finalScore,
diff --git a/frontend/app/creator/page.tsx b/frontend/app/creator/page.tsx
index 6829bbd..4ed6fa3 100644
--- a/frontend/app/creator/page.tsx
+++ b/frontend/app/creator/page.tsx
@@ -82,7 +82,7 @@ function mapTaskResponseToUI(task: TaskResponse): Task {
     id: task.id,
     title: task.name,
     description: `${task.project.name} · ${ui.statusLabel}`,
-    platform: 'douyin', // 后端暂无平台字段，默认
+    platform: task.project?.platform || 'douyin',
     scriptStage: ui.scriptStage,
     videoStage: ui.videoStage,
     buttonText: ui.buttonText,
diff --git a/frontend/types/task.ts b/frontend/types/task.ts
index 2b7c45c..96acb0f 100644
--- a/frontend/types/task.ts
+++ b/frontend/types/task.ts
@@ -29,6 +29,7 @@ export interface ProjectInfo {
   id: string
   name: string
   brand_name?: string | null
+  platform?: string | null
 }
 
 export interface AgencyInfo {