protected void Page_Load(object sender, EventArgs e)
    {
        StringBuilder sb = new StringBuilder();
        sb.Append("<table cellspacing=\"0\" cellpadding=\"0\" border=\"0\" style=\"width: 714px; height: 86px;\">");
        sb.Append("<tbody>");
        sb.Append("<tr>");
        sb.Append("<td valign=\"top\"><br />");
        sb.Append("asdasdsadasdsadsa<br />");
        sb.Append("asdsdasdadsdsddsadasdasdasdsa");
        sb.Append("<img width=\"309\" height=\"46\" src=\"/website/UpFile/image/box_1.png\" alt=\"\" /></td>");
        sb.Append("</tr>");
        sb.Append("</tbody>");
        sb.Append("</table>");
        string pattern = @"(?is)<img\s*[^>]*>";
        System.Text.RegularExpressions.Regex reg = new System.Text.RegularExpressions.Regex(pattern);
        string result = reg.Replace(sb.ToString(), "");
    }