protected string str = "<table><tr><td>sdasasdsdd</td></tr></table><br><p>sds</p><img id='img1' src='http://www.baidu.com/img/baidu_logo.gif' width='100' height='50' alt=''>aaassss<br><img src='http://www.baidu.com/img/baidu_logo.gif' width='100' height='50' alt=''> 說是道 ";

protected void Page_Load(object sender, EventArgs e)

{

//string regexstr = @"<[^>]*>"; //去除所有的標籤

//@"<script[^>]*?>.*?</script >" //去除所有指令碼，中間部分也刪除

// string regexstr = @"<img[^>]*>"; //去除圖片的正則

// string regexstr = @"<(?!br).*?>"; //去除所有標籤，只剩br

// string regexstr = @"<table[^>]*?>.*?</table>"; //去除table裡面的所有內容

string regexstr = @"<(?!img|br|p|/p).*?>"; //去除所有標籤，只剩img,br,p

str = Regex.Replace(str, regexstr, string.Empty, RegexOptions.IgnoreCase);

}