引用新浪天气预报http://community.youkuaiyun.com/

private void Page_Load(object sender, System.EventArgs e)
 {
  HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://weather.sina.com.cn/iframe/weather/210201_w.html");
  request.Method = "Get";
  request.ContentType = "application/x-www-form-urlencoded";
  WebResponse response = request.GetResponse();
  Stream s = response.GetResponseStream();
  StreamReader sr = new StreamReader(s,System.Text.Encoding.GetEncoding("GB2312"));
  string html = sr.ReadToEnd();
  s.Close();
  sr.Close();

  int start = html.IndexOf("<br>");
  html = html.Substring(start + 4);

  int end = html.IndexOf("</td>");
  html = html.Substring(0,end);

  htmResult = html;

}