c# post html代码


HtmlText = "<b>你好</b>";//中文，html代码有问题
            try
            {
                HttpWebRequest req = (HttpWebRequest)WebRequest.Create(Url);
                req.Accept = "application/x-shockwave-flash, image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, */*";
                req.Referer = Url;
                req.ContentType = "application/x-www-form-urlencoded";
                req.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 2.0.50727; MAXTHON 2.0)";
                req.KeepAlive = true;
                req.Method = "POST";
                string PostStr = "FileName=" + FileName + "&HtmlText=" + HtmlText + "";
                ASCIIEncoding ASC2E = new ASCIIEncoding();
                byte[] bytePost = ASC2E.GetBytes(PostStr);//把要发送的数据变成字节
                req.ContentLength = bytePost.Length;
                //下面是发送数据的字节流
                Stream MyStream = req.GetRequestStream();
                MyStream.Write(bytePost, 0, bytePost.Length);
                MyStream.Close();
                //创建HttpWebResponse实例
                HttpWebResponse hwrp = (HttpWebResponse)req.GetResponse();
                StreamReader MyStreamR = new StreamReader(hwrp.GetResponseStream(), Encoding.Default);
                string result = MyStreamR.ReadToEnd();
                MyStreamR.Close();
            }
            catch (Exception e)
            {
                MessageBox.Show(e.ToString());
                Error(ErrorStatus.UpdateError);
            }
我想用 post 方法传值到一个网页,可是怎么传 带标记的代码呢，就象这个 HtmlText = "<b>你好</b>" .现在传这个都会在创建HttpWebResponse实例 的时候报错.