今天刚给别人做了一个DOME,你把我的[]替换成你的<p>就ok了
static void Main()
        {
            //匹配页面上所以的符合格式的字符串
            Regex x = new Regex("\\[[^(\\])]*\\][^(\\])]*(.*)[^(\\])]*\\[\\/[^\\]]*[\\]]");

            //测试字符串
            var str = "[tex=6.6875x1.0625]23424[/tex]sadasdasdasdadadasdadasda";
            //符合条件的如newStr[0]=[tex=6.6875x1.0625]23424[/tex]
            var newStr = x.Matches(str);
            if (newStr.Count > 0)
                foreach (var s0 in newStr)
            {
                string s1 = Regex.Replace(s0.ToString(), "\\[/(.*)\\]", "");
                string s2 = Regex.Replace(s1.ToString(), "\\[(.*)\\]", "");
                Console.WriteLine(s2);
            }
                    
            Console.ReadKey();