winfrom(C#) Post提交(带参数)，返回值

public void PostMoths()
        {
            string strURL = "http://www.cqjg.gov.cn/newwww/c7/clwz.asp";
            System.Net.HttpWebRequest request;
            request = (System.Net.HttpWebRequest)WebRequest.Create(strURL);
            //Post请求方式
            request.Method = "POST";
            //内容类型
            request.ContentType = "application/x-www-form-urlencoded";
            //参数经过URL编码
            string paraUrlCoded = System.Web.HttpUtility.UrlEncode("LicenseTxt");
            paraUrlCoded += "=" + System.Web.HttpUtility.UrlEncode(txtCarId .Text.Trim());
            paraUrlCoded +="& "+ System.Web.HttpUtility.UrlEncode("VIN");
            paraUrlCoded += "=" + System.Web.HttpUtility.UrlEncode(txtCarNumber.Text.Trim());
            byte[] payload;
            //将URL编码后的字符串转化为字节
            payload = System.Text.Encoding.UTF8.GetBytes(paraUrlCoded);
            //设置请求的ContentLength 
            request.ContentLength = payload.Length;
            //获得请求流
            Stream writer = request.GetRequestStream();
            //将请求参数写入流
            writer.Write(payload, 0, payload.Length);
            //关闭请求流
            writer.Close();
            System.Net.HttpWebResponse response;
            //获得响应流
            response = (System.Net.HttpWebResponse)request.GetResponse();
            System.IO.Stream s;
            s = response.GetResponseStream();
            string StrDate = "";
            string strValue = "";
            StreamReader Reader = new StreamReader(s,Encoding.Default);
            while ((StrDate= Reader.ReadLine())!=null)
            {
                strValue += StrDate+"\r\n";
            }
            // txtInfo.Text = strValue;
            txtInfo.Text= FindContent(strValue);
            //XmlTextReader Reader = new XmlTextReader(s);
            //Reader.MoveToContent();
            //string strValue = Reader.ReadInnerXml();
            //strValue = strValue.Replace("<", "<");
            //strValue = strValue.Replace(">", ">");
            //MessageBox.Show(strValue);
            //Reader.Close();
        }