string url ="http://www.baidu.com/s?tn=sitehao123&bs=%B3%B5%BC%D1&f=8&rsv_bp=1&wd=%B3%B5%BC%D1&inputT=0";
Regex urlRegex =new Regex(@"(?:^|/?|&)wd=([^&]*)(?:&|$)");
Match m = urlRegex.Match(url);
string result =string.Empty;
if (m.Success)
{
result = m.Groups[1].Value;
Console.Write(m.Groups[1].Value);
}