C# WebService服务Post提交

public string WebServerTest(string PostData)
        {
            PostData = "jsonData=" + PostData;
            string POSTURL = "http://101.201.78.100:8888/ChannelWebService.asmx/CheckIsConnected";
            Encoding myEncoding = Encoding.GetEncoding("UTF-8"); ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3; //将提交的字符串数据转换成字节数组 //注意提交的编码,这里默认的是Default：系统当前编码 
            byte[] postData = myEncoding.GetBytes(PostData); //设置提交的相关参数 
            HttpWebRequest request = WebRequest.Create(POSTURL) as HttpWebRequest; //实例化一个证书 
            //X509Certificate2 cerCaiShang = GetCertificate(); ServicePointManager.ServerCertificateValidationCallback = (sender, certificate, chain, sslPolicyErrors) => true; 
            //request.ClientCertificates.Add(cerCaiShang); 
            request.Method = "POST"; request.KeepAlive = true;
            //request.AllowAutoRedirect = true;
            request.ProtocolVersion = HttpVersion.Version10;
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;
            request.ContentType = "text/xml;charset=utf-8";
            request.ContentType = "application/x-www-form-urlencoded";
            request.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 2.0.50727; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)";
            CookieContainer cookieContainer = new CookieContainer();
            request.CookieContainer = cookieContainer;
            request.ContentLength = postData.Length;
            #region 传输数据
            try { using (Stream writer = request.GetRequestStream()) { writer.Write(postData, 0, postData.Length); } }
            catch (Exception ex) { return ex.Message; }
            #endregion
            #region 接收返回的数据
            string srcString = string.Empty; try { HttpWebResponse response = request.GetResponse() as HttpWebResponse; using (Stream sr = response.GetResponseStream()) { using (StreamReader reader = new StreamReader(sr, myEncoding)) { srcString = reader.ReadToEnd(); } } }
            catch (Exception ex) { return ex.Message; }
            #endregion
            return srcString;
        }