public static string ReplaceHtmlTag(string html, int length = 0)
{
    string strText = System.Text.RegularExpressions.Regex.Replace(html, "<[^>]+>", "");
    strText = System.Text.RegularExpressions.Regex.Replace(strText, "&[^;]+;", "");

    if (length > 0  && strText.Length > length)
        return strText.Substring(0, length);

    return strText;
}

转载自：http://www.cnblogs.com/youring2/archive/2013/04/03/2997826.html

参考页面：

http://www.yuanjiaocheng.net/CSharp/Csharp-stringbuilder.html

http://www.yuanjiaocheng.net/CSharp/csharp-array.html

http://www.yuanjiaocheng.net/CSharp/Csharp-multi-dimensional-array.html

http://www.yuanjiaocheng.net/CSharp/Csharp-jagged-array.html

http://www.yuanjiaocheng.net/CSharp/Csharp-collection.html

C#去除HTML标签