public static string DelHtml(this string Htmlstring)
    {

        //删除脚本   
        Htmlstring = Regex.Replace(Htmlstring, @"<script(\s[^>]*?)?>[\s\S]*?</script>", "", RegexOptions.IgnoreCase);
        //删除样式  
        Htmlstring = Regex.Replace(Htmlstring, @"<style>[\s\S]*?</style>", "", RegexOptions.IgnoreCase);
        //删除html标签
        Htmlstring = Regex.Replace(Htmlstring, @"<(.[^>]*)>", "", RegexOptions.IgnoreCase);
        return Htmlstring;

    }

------解决方案--------------------
你把< 和 > 等关键字符转义一下就行了.
比如 < , 转义成 &lt; 存到数据库,读取的时候, &lt; 就会自动转义成 < 了.

------解决方案--------------------
C# code

/// <summary>
        /// HTML标签过滤
        /// </summary>
        /// <param name="strHtml">需要过滤的字符串</param>
        /// <returns></returns>
        public static string StripHTML(string strHtml)
        {
            string[] aryReg ={
                                  @"<script[^>]*?>.*?</script>",

                                  @"<(\/\s*)?!?((\w+:)?\w+)(\w+(\s*=?\s*(([""'])(\\[""'tbnr]|[^\7])*?\7|\w+)|.{0})|\s)*?(\/\s*)?>",
                                  @"([\r\n])[\s]+",
                                  @"&(quot|#34);",
                                  @"&(amp|#38);",
                                  @"&(lt|#60);",
                                  @"&(gt|#62);", 
                                  @"&(nbsp|#160);", 
                                  @"&(iexcl|#161);",
                                  @"&(cent|#162);",
                                  @"&(pound|#163);",
                                  @"&(copy|#169);",
                                  @"&#(\d+);",
                                  @"-->",
                                  @"<!--.*\n"
                              };

            string[] aryRep = {
                                   "",
                                   "",
                                   "",
                                   "\"",
                                   "&",
                                   "<",
                                   ">",
                                   " ",
                                   "\xa1",//chr(161),
                                   "\xa2",//chr(162),
                                   "\xa3",//chr(163),
                                   "\xa9",//chr(169),
                                   "",
                                   "\r\n",
                                   ""
                               };

            string newReg = aryReg[0];
            string strOutput = strHtml;
            for (int i = 0; i < aryReg.Length; i++)
            {
                System.Text.RegularExpressions.Regex regex = new System.Text.RegularExpressions.Regex(aryReg[i], System.Text.RegularExpressions.RegexOptions.IgnoreCase);
                strOutput = regex.Replace(strOutput, aryRep[i]);
            }
            strOutput.Replace("<", "");
            strOutput.Replace(">", "");
            strOutput = strOutput.Replace("\r\n", "");
            return strOutput;
        }

------解决方案-----