diff --git a/packages/services/conversation-service/src/infrastructure/agents/coordinator/coordinator-agent.service.ts b/packages/services/conversation-service/src/infrastructure/agents/coordinator/coordinator-agent.service.ts
index 6a37a09..507ff16 100644
--- a/packages/services/conversation-service/src/infrastructure/agents/coordinator/coordinator-agent.service.ts
+++ b/packages/services/conversation-service/src/infrastructure/agents/coordinator/coordinator-agent.service.ts
@@ -330,57 +330,99 @@ export class CoordinatorAgentService implements OnModuleInit {
 
   /** 文本类文件最大嵌入大小 (超过则截断) */
   private readonly MAX_TEXT_EMBED_SIZE = 50_000;
+  /** 二进制文件最大 base64 大小 (20MB，Claude API 限制) */
+  private readonly MAX_BINARY_SIZE = 20 * 1024 * 1024;
+
+  /**
+   * 获取 file-service 内部地址
+   * conversation-service 与 file-service 同在 Docker 网络内，
+   * 通过 service name + port 直连。
+   */
+  private get fileServiceBaseUrl(): string {
+    return this.configService.get<string>('FILE_SERVICE_URL') || 'http://file-service:3006';
+  }
 
   /**
    * 将附件转换为 Claude API content blocks
-   * - image → { type: 'image', source: { type: 'url', url } }
-   * - PDF   → { type: 'document', source: { type: 'url', url }, title }
-   * - text/csv/json/md → 下载内容嵌入为 text block（Claude 无法自行访问 URL）
+   *
+   * 核心策略：通过 file-service 内部 API 下载文件后转 base64 发给 Claude。
+   * 使用 att.id 构建内部 URL（/files/:id/content），绕过 MinIO presigned URL
+   * 的 Docker 内部主机名问题（minio:9000 在外网不可达）。
+   *
+   * - image → 下载 → base64 image block
+   * - PDF   → 下载 → base64 document block
+   * - text/csv/json/md → 下载 → 嵌入文本 text block
+   * - Office (docx/xlsx) → 暂不支持，提示用户
    */
   private async buildAttachmentBlocks(attachments: FileAttachment[]): Promise<any[]> {
     const blocks: any[] = [];
 
     for (const att of attachments) {
-      if (!att.downloadUrl) continue;
+      // 通过 file-service 内部 API 下载，不依赖 downloadUrl
+      // file-service 使用 globalPrefix 'api/v1'，完整路径: /api/v1/files/:id/content
+      const contentUrl = `${this.fileServiceBaseUrl}/api/v1/files/${att.id}/content`;
 
-      if (att.type === 'image') {
-        blocks.push({
-          type: 'image',
-          source: { type: 'url', url: att.downloadUrl },
-        });
-      } else if (att.mimeType === 'application/pdf') {
-        // Claude 原生支持 PDF 文档
-        blocks.push({
-          type: 'document',
-          source: { type: 'url', url: att.downloadUrl },
-          title: att.originalName,
-        });
-      } else if (this.isTextBasedMime(att.mimeType)) {
-        // 文本类文件：下载内容并直接嵌入
-        try {
-          const textContent = await this.fetchTextContent(att.downloadUrl);
+      try {
+        if (att.type === 'image') {
+          const { base64, mediaType } = await this.downloadAsBase64(contentUrl, att.mimeType);
+          blocks.push({
+            type: 'image',
+            source: { type: 'base64', media_type: mediaType, data: base64 },
+          });
+        } else if (att.mimeType === 'application/pdf') {
+          const { base64 } = await this.downloadAsBase64(contentUrl, att.mimeType);
+          blocks.push({
+            type: 'document',
+            source: { type: 'base64', media_type: 'application/pdf', data: base64 },
+            title: att.originalName,
+          });
+        } else if (this.isTextBasedMime(att.mimeType)) {
+          const textContent = await this.fetchTextContent(contentUrl);
           blocks.push({
             type: 'text',
             text: `--- 附件: ${att.originalName} ---\n${textContent}`,
           });
-        } catch (err) {
-          this.logger.warn(`Failed to fetch text content for ${att.originalName}: ${err}`);
+        } else {
+          // Office 文档等暂不支持
           blocks.push({
             type: 'text',
-            text: `[附件: ${att.originalName} — 内容加载失败]`,
+            text: `[附件: ${att.originalName} (${att.mimeType}) — 该格式暂不支持AI解析，请转为PDF后重新上传]`,
           });
         }
+      } catch (err) {
+        this.logger.warn(`Failed to process attachment ${att.originalName}: ${err}`);
+        blocks.push({
+          type: 'text',
+          text: `[附件: ${att.originalName} — 内容加载失败]`,
+        });
       }
     }
 
     return blocks;
   }
 
-  /** 通过预签名 URL 获取文本文件内容 */
+  /**
+   * 从内部 URL 下载文件并转为 base64
+   * conversation-service 与 file-service 同在 Docker 网络内
+   */
+  private async downloadAsBase64(url: string, mimeType: string): Promise<{ base64: string; mediaType: string }> {
+    const response = await fetch(url);
+    if (!response.ok) {
+      throw new Error(`HTTP ${response.status} from ${url}`);
+    }
+    const arrayBuffer = await response.arrayBuffer();
+    if (arrayBuffer.byteLength > this.MAX_BINARY_SIZE) {
+      throw new Error(`文件过大 (${(arrayBuffer.byteLength / 1024 / 1024).toFixed(1)}MB)，超过 ${this.MAX_BINARY_SIZE / 1024 / 1024}MB 限制`);
+    }
+    const base64 = Buffer.from(arrayBuffer).toString('base64');
+    return { base64, mediaType: mimeType };
+  }
+
+  /** 从内部 URL 获取文本文件内容 */
   private async fetchTextContent(url: string): Promise<string> {
     const response = await fetch(url);
     if (!response.ok) {
-      throw new Error(`HTTP ${response.status}`);
+      throw new Error(`HTTP ${response.status} from ${url}`);
     }
     const text = await response.text();
     if (text.length > this.MAX_TEXT_EMBED_SIZE) {
diff --git a/packages/services/file-service/src/adapters/inbound/file.controller.ts b/packages/services/file-service/src/adapters/inbound/file.controller.ts
index 3a2459d..d3279c0 100644
--- a/packages/services/file-service/src/adapters/inbound/file.controller.ts
+++ b/packages/services/file-service/src/adapters/inbound/file.controller.ts
@@ -6,6 +6,7 @@ import {
   Param,
   Body,
   Query,
+  Res,
   UploadedFile,
   UseInterceptors,
   Headers,
@@ -13,6 +14,7 @@ import {
   HttpCode,
   HttpStatus,
 } from '@nestjs/common';
+import type { Response } from 'express';
 import { FileInterceptor } from '@nestjs/platform-express';
 import { FileService } from '../../application/services/file.service';
 import {
@@ -89,6 +91,36 @@ export class FileController {
     return { url };
   }
 
+  /**
+   * 直接获取文件内容（流式代理）
+   * 前端通过此端点访问文件，避免暴露 MinIO 内部 URL
+   */
+  @Get(':id/content')
+  async getFileContent(
+    @Param('id', ParseUUIDPipe) fileId: string,
+    @Res() res: Response,
+  ): Promise<void> {
+    const { buffer, mimeType, originalName } = await this.fileService.getFileContent(fileId);
+    res.setHeader('Content-Type', mimeType);
+    res.setHeader('Content-Disposition', `inline; filename="${encodeURIComponent(originalName)}"`);
+    res.setHeader('Cache-Control', 'public, max-age=3600');
+    res.send(buffer);
+  }
+
+  /**
+   * 获取缩略图内容
+   */
+  @Get(':id/thumbnail')
+  async getThumbnail(
+    @Param('id', ParseUUIDPipe) fileId: string,
+    @Res() res: Response,
+  ): Promise<void> {
+    const { buffer } = await this.fileService.getThumbnailContent(fileId);
+    res.setHeader('Content-Type', 'image/webp');
+    res.setHeader('Cache-Control', 'public, max-age=86400');
+    res.send(buffer);
+  }
+
   /**
    * 获取用户的所有文件
    */
diff --git a/packages/services/file-service/src/application/services/file.service.ts b/packages/services/file-service/src/application/services/file.service.ts
index 6548dc5..9092b05 100644
--- a/packages/services/file-service/src/application/services/file.service.ts
+++ b/packages/services/file-service/src/application/services/file.service.ts
@@ -243,6 +243,37 @@ export class FileService {
     return this.toResponseDto(file);
   }
 
+  /**
+   * 直接获取文件内容（流式代理，不依赖预签名 URL）
+   * 无需 userId 验证 — 通过 fileId (UUID) 本身作为不可猜测的访问令牌
+   */
+  async getFileContent(fileId: string): Promise<{ buffer: Buffer; mimeType: string; originalName: string }> {
+    const file = await this.fileRepo.findById(fileId);
+    if (!file || !file.isReady()) {
+      throw new NotFoundException('File not found');
+    }
+
+    const buffer = await this.storageAdapter.downloadFile(file.storagePath);
+    return {
+      buffer,
+      mimeType: file.mimeType,
+      originalName: file.originalName,
+    };
+  }
+
+  /**
+   * 获取缩略图内容
+   */
+  async getThumbnailContent(fileId: string): Promise<{ buffer: Buffer }> {
+    const file = await this.fileRepo.findById(fileId);
+    if (!file || !file.isReady() || !file.thumbnailPath) {
+      throw new NotFoundException('Thumbnail not found');
+    }
+
+    const buffer = await this.storageAdapter.downloadFile(file.thumbnailPath);
+    return { buffer };
+  }
+
   /**
    * 获取文件下载 URL
    */
@@ -273,7 +304,7 @@ export class FileService {
       conversationId,
     );
 
-    return Promise.all(files.map((f) => this.toResponseDto(f)));
+    return files.map((f) => this.toResponseDto(f));
   }
 
   /**
@@ -348,8 +379,11 @@ export class FileService {
 
   /**
    * 转换为响应 DTO
+   *
+   * downloadUrl / thumbnailUrl 使用 API 代理路径 /api/v1/files/:id/content
+   * 而非 MinIO presigned URL（Docker 内部 hostname，外网不可达）
    */
-  private async toResponseDto(file: FileEntity): Promise<FileResponseDto> {
+  private toResponseDto(file: FileEntity): FileResponseDto {
     const dto: FileResponseDto = {
       id: file.id,
       originalName: file.originalName,
@@ -361,16 +395,11 @@ export class FileService {
     };
 
     if (file.isReady()) {
-      dto.downloadUrl = await this.storageAdapter.getPresignedUrl(
-        file.storagePath,
-        3600,
-      );
+      // 使用 API 代理路径，浏览器通过 nginx → Kong → file-service 访问
+      dto.downloadUrl = `/api/v1/files/${file.id}/content`;
 
       if (file.thumbnailPath) {
-        dto.thumbnailUrl = await this.storageAdapter.getPresignedUrl(
-          file.thumbnailPath,
-          3600,
-        );
+        dto.thumbnailUrl = `/api/v1/files/${file.id}/thumbnail`;
       }
     }