string test = "<a id=\"biz_Server\" href=\"/a.shtml?&ga=1111&gs=2222\">谢谢</a>";
Match m = Regex.Match(test, @"<a[^>]*ga=(?<ga>\d{4})[^>]*gs=(?<gs>\d{4})[^>]*>(?<text>[^<]*)</a>", RegexOptions.IgnoreCase);
if (m.Success)
{
MessageBox.Show(m.Groups["text"].Value);
MessageBox.Show(m.Groups["ga"].Value);
MessageBox.Show(m.Groups["gs"].Value);
}