string source = @"<div id=""a"" class=""b"">";
            Regex reg = new Regex(@"(id=""\S*"")|(class=""\S*"")");
            source = reg.Replace(source, "");

------解决方案--------------------


C# code

 static void Main(string[] args)
            {
                string str = @"<div id=""a"" class=""b"">
  <ul class=""m"">
  <table>
  <tr class=""on"" id=""role"">";

                Regex re = new Regex(@"(id=""[^""]+"")|(class=""[^""]+"")", RegexOptions.None);
                str = re.Replace(str, "");
                Console.WriteLine(str);
                Console.ReadLine();
                                              
            }