string url = "网址";
   HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
   string s = "要提交的数据";
   byte[] requestBytes = System.Text.Encoding.ASCII.GetBytes (LoginInfo);
   req.Method = "POST";
   req.ContentType = "application/x-www-form-urlencoded";
   req.ContentLength = requestBytes.Length;
   Stream requestStream = req.GetRequestStream();
   requestStream.Write(requestBytes,0,requestBytes.Length);
   requestStream.Close();

   HttpWebResponse res = (HttpWebResponse)req.GetResponse();
   StreamReader sr = new StreamReader(res.GetResponseStream(), System.Text.Encoding.Default);
   string backstr = sr.ReadToEnd();
   Response.Write(line);
   sr.Close();
   res.Close();