diff --git a/src/Qiniu/Http/HttpManager.cs b/src/Qiniu/Http/HttpManager.cs
index b1098f9..3d202de 100644
--- a/src/Qiniu/Http/HttpManager.cs
+++ b/src/Qiniu/Http/HttpManager.cs
@@ -112,14 +112,15 @@ public HttpResult Get(string url, StringDictionary headers, string token, bool b
                 wReq.Method = "GET";
                 if (headers != null)
                 {
-                    foreach (string fieldName in headers.Keys)
+                    if (headers.ContainsKey("Content-Type"))
                     {
-                        wReq.Headers.Add(fieldName, headers[fieldName]);
+                        wReq.ContentType = headers["Content-Type"];
+                        headers.Remove("Content-Type");
                     }
 
-                    if (headers.ContainsKey("Content-Type"))
+                    foreach (string fieldName in headers.Keys)
                     {
-                        wReq.ContentType = headers["Content-Type"];
+                        wReq.Headers.Add(fieldName, headers[fieldName]);
                     }
                 }
                 if (!string.IsNullOrEmpty(token))
@@ -262,14 +263,15 @@ public HttpResult Post(string url, StringDictionary headers, string token, bool
                 wReq.Method = "POST";
                 if (headers != null)
                 {
-                    foreach (string fieldName in headers.Keys)
+                    if (headers.ContainsKey("Content-Type"))
                     {
-                        wReq.Headers.Add(fieldName, headers[fieldName]);
+                        wReq.ContentType = headers["Content-Type"];
+                        headers.Remove("Content-Type");
                     }
 
-                    if (headers.ContainsKey("Content-Type"))
+                    foreach (string fieldName in headers.Keys)
                     {
-                        wReq.ContentType = headers["Content-Type"];
+                        wReq.Headers.Add(fieldName, headers[fieldName]);
                     }
                 }
                 if (!string.IsNullOrEmpty(token))