diff --git a/src/Oms.Application/Services/Storage/FileStorageService.cs b/src/Oms.Application/Services/Storage/FileStorageService.cs
index f2d91b0..016b3b2 100644
--- a/src/Oms.Application/Services/Storage/FileStorageService.cs
+++ b/src/Oms.Application/Services/Storage/FileStorageService.cs
@@ -108,6 +108,55 @@ public class FileStorageService : ApplicationService
         var key = FileStorage.ToStorageKey(input.PathOrUrl);
         return new NormalizeKeyOutput { Key = key };
     }
+
+    /// <summary>
+    /// 按 key / URL 流式读取文件（供面单预览等场景，避免前端跨域 iframe 空白）。
+    /// </summary>
+    [HttpGet("/file-storage/stream")]
+    public async Task<IActionResult> StreamAsync([FromQuery] string key, CancellationToken cancellationToken = default)
+    {
+        if (string.IsNullOrWhiteSpace(key))
+        {
+            throw new BusinessException("key 不能为空");
+        }
+
+        string storageKey;
+        try
+        {
+            storageKey = FileStorage.ToStorageKey(key) ?? FileStoragePath.NormalizeKey(key);
+        }
+        catch (Exception)
+        {
+            throw new BusinessException("无法解析文件 key");
+        }
+
+        if (!await FileStorage.ExistsAsync(storageKey, cancellationToken))
+        {
+            throw new BusinessException("文件不存在或已过期");
+        }
+
+        var stream = await FileStorage.OpenReadAsync(storageKey, cancellationToken);
+        return new FileStreamResult(stream, GuessStreamContentType(storageKey))
+        {
+            EnableRangeProcessing = true,
+        };
+    }
+
+    private static string GuessStreamContentType(string storageKey)
+    {
+        if (storageKey.EndsWith(".pdf", StringComparison.OrdinalIgnoreCase))
+        {
+            return "application/pdf";
+        }
+
+        if (storageKey.EndsWith(".html", StringComparison.OrdinalIgnoreCase)
+            || storageKey.EndsWith(".htm", StringComparison.OrdinalIgnoreCase))
+        {
+            return "text/html; charset=utf-8";
+        }
+
+        return "application/octet-stream";
+    }
 }
 
 public class PresignUploadInput