using System;

using System.Collections.Generic;

using Newtonsoft.Json;

public class Program

{

    public class MyData

    {

        public List<List<KeyValuePair<string, string>>> Data { get; set; }

    }

    public static void Main()

    {

        string data = "{\"Data\": [[{ \"Key\": \"Proudct\", \"Value\": \"PC\" }, { \"Key\": \"Address\", \"Value\": \"USA\" }, { \"Key\": \"Tel\", \"Value\": \"123456777\" }]]}";

        MyData mydata = JsonConvert.DeserializeObject<MyData>(data);

        Console.WriteLine(Newtonsoft.Json.JsonConvert.SerializeObject(mydata));

    }

}