JavaScriptSerializer jss = new JavaScriptSerializer();

------解决方案--------------------

C# code


 public static void Main()
        {

            string json = "{\"sign\":1,\"data\":"+
                            "{\"12400000\":{\"role_id\":12400000,\"role_name\":\"s1.\u8863\u53ca\u6cab\",\"role_level\":2}" +
                            ",\"12400001\":{\"role_id\":12400001,\"role_name\":\"s2.\u8863\u53ca\u6cab\",\"role_level\":2}"+
                            ",\"12400002\":{\"role_id\":12400000,\"role_name\":\"s1.\u8863\u53ca\u6cab\",\"role_level\":2}}}";


            var o = JObject.Parse(json);

            foreach (JToken child in o["data"].Children())
            {
                foreach (JToken grandChild in child)
                {
                    if (grandChild["role_name"].ToString().StartsWith("s2."))
                    {
                        Console.WriteLine(grandChild["role_id"].ToString());
                    }
                        
                }
            }
            Console.ReadLine();

        }

------解决方案--------------------
sorry，忘了还要判断12400001

C# code


 public static void Main()
        {

            string json = "{\"sign\":1,\"data\":"+
                            "{\"12400000\":{\"role_id\":12400000,\"role_name\":\"s1.\u8863\u53ca\u6cab\",\"role_level\":2}" +
                            ",\"12400001\":{\"role_id\":12400001,\"role_name\":\"s2.\u8863\u53ca\u6cab\",\"role_level\":2}"+
                            ",\"12400002\":{\"role_id\":12400000,\"role_name\":\"s1.\u8863\u53ca\u6cab\",\"role_level\":2}}}";


            var o = JObject.Parse(json);

            foreach (JToken child in o["data"].Children())
            {
                var property = child as JProperty;

                if (property.Name.Equals("12400001"))
                {
                    foreach (JToken grandChild in child)
                    {
                        if (grandChild["role_name"].ToString().StartsWith("s2.")