//通过Post发送的数据
   string payload="chkbook=book&keyword=管理";
   WebRequest req = WebRequest.Create("");
   req.Method = "POST";
   req.ContentType = "application/x-www-form-urlencoded";
   StringBuilder UrlEncoded = new StringBuilder();
   Char[] reserved = {'?', '=', '&'};
   byte[] SomeBytes = null;
   if (payload != null)
   {
    int i=0, j;
    while(i    {
     j=payload.IndexOfAny(reserved, i);
     if (j==-1)
     {
      UrlEncoded.Append(HttpUtility.UrlEncode(payload.Substring(i, payload.Length-i),System.Text .Encoding .GetEncoding ("gb2312")));
      break;
     }
     UrlEncoded.Append(HttpUtility.UrlEncode(payload.Substring(i, j-i),System.Text .Encoding .GetEncoding ("gb2312")));
     UrlEncoded.Append(payload.Substring(j,1));
     i = j+1;
    }
    SomeBytes = Encoding.Default.GetBytes(UrlEncoded.ToString());
    req.ContentLength = SomeBytes.Length;
    Stream newStream = req.GetRequestStream();
    newStream.Write(SomeBytes, 0, SomeBytes.Length);
    newStream.Close();
   }
   else
   {
    req.ContentLength = 0;
   }
   try
   {
    WebResponse result = req.GetResponse();
    Stream ReceiveStream = result.GetResponseStream();

    Byte[] read = new Byte[512];
    int bytes = ReceiveStream.Read(read, 0, 512);

    txtHTML.InnerHtml = "";
    while (bytes > 0)
    {

     // 注意：
     // 下面假定响应使用 UTF-8 作为编码方式。
     // 如果内容以 ANSI 代码页形式（例如，932）发送，则使用类似下面的语句：
     //  Encoding encode = System.Text.Encoding.GetEncoding("shift-jis");
     Encoding encode = System.Text.Encoding.GetEncoding("gb2312");
     txtHTML.InnerHtml = txtHTML.InnerHtml + encode.GetString(read, 0, bytes);
     bytes = ReceiveStream.Read(read, 0, 512);
    }
   }
   catch(Exception)
   {
    txtHTML.InnerHtml = "检索页时出错";
   }

出处：狂风之家 BLOG