StringBuilder sb = new StringBuilder("data=1");

byte[] bytes = Encoding.UTF8.GetBytes(sb.ToString());

WebRequest req = WebRequest.Create("http://baidu.com?");

req.Method = "POST";

req.ContentType = "application/x-www-form-urlencoded";

req.ContentLength = bytes.Length;

Stream reqSt = req.GetRequestStream();

reqSt.Write(bytes, 0, bytes.Length);

reqSt.Close();

WebResponse rep = req.GetResponse();

Stream st = rep.GetResponseStream();

StreamReader reader = new StreamReader(st);

string txt = reader.ReadToEnd();

reader.Close(); st.Close();

}