//using (System.Net.WebClient wc = new System.Net.WebClient())

//{

//    wc.Encoding = Encoding.GetEncoding("GB2312");

//    NameValueCollection postData = new NameValueCollection();

//    postData.Add("UserIDText", userId.ToString());

//    postData.Add("UserNameText", userName);

//    postData.Add("ContentText", HttpUtility.UrlEncode(content,wc.Encoding));

//    postData.Add("UrlText", url);

//    wc.Headers.Add(HttpRequestHeader.ContentEncoding, "gb23112");

//    wc.Headers.Add(HttpRequestHeader.ContentType, "application/x-www-form-urlencoded");

//    wc.UploadValues(new Uri(postUrl),"POST", postData);

//}

Encoding myEncoding = Encoding.GetEncoding("gb2312");

string param = "UserIDText=" + HttpUtility.UrlEncode(userId.ToString(), myEncoding)

    + "&" + "UserNameText=" + HttpUtility.UrlEncode(userName, myEncoding)

    + "&" + "ContentText=" + HttpUtility.UrlEncode(content, myEncoding)

    + "&" + "UrlText=" + HttpUtility.UrlEncode(url, myEncoding);

byte[] postBytes = Encoding.ASCII.GetBytes(param);

HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(postUrl);

req.Method = "POST";

req.ContentType = "application/x-www-form-urlencoded;charset=gb2312";

req.ContentLength = postBytes.Length;

using (Stream reqStream = req.GetRequestStream())

{

    reqStream.Write(postBytes, 0, postBytes.Length);

}

using (WebResponse wr = req.GetResponse())

{

    //在这里对接收到的页面内容进行处理

}