diff --git a/server/MiAssessment/src/MiAssessment.Core/Services/UploadConfigService.cs b/server/MiAssessment/src/MiAssessment.Core/Services/UploadConfigService.cs
index e891a87..aa22b26 100644
--- a/server/MiAssessment/src/MiAssessment.Core/Services/UploadConfigService.cs
+++ b/server/MiAssessment/src/MiAssessment.Core/Services/UploadConfigService.cs
@@ -73,9 +73,9 @@ public class UploadConfigService : IUploadConfigService
         var policy = GeneratePostPolicy(objectKey, setting.AccessKeyId!, keyTime);
         var policyBase64 = Convert.ToBase64String(Encoding.UTF8.GetBytes(policy));
 
-        // 生成签名: SignKey -> StringToSign -> Signature
+        // 生成签名: SignKey -> StringToSign(SHA1 of raw policy) -> Signature
         var signKey = HmacSha1(setting.AccessKeySecret!, keyTime);
-        var stringToSign = Sha1Hash(policyBase64);
+        var stringToSign = Sha1Hash(policy);
         var signature = HmacSha1(signKey, stringToSign);
 
         _logger.LogInformation("生成POST Object签名成功: {ObjectKey}", objectKey);