Code
public class OnlineUserModel
{
    public OnlineUserModel()
    {
        //
        // TODO: Add constructor logic here

        //
       
    }
    public string Callednumber{get;set;}
    public int Total{get;set;}
    public List<ProvinceUser> Provinces { get; set; }
    

}

public class ProvinceUser
{

    public string ProvinceName { get; set; }
    public int ProvinceCount { get; set; }
    public List<CityUser> Citys { get; set; }
}

public class CityUser
{

    public string CityName { get; set; }
    public int CityCount { get; set; }
}

Code
        DataTable dt = getData(TextBox1.Text.ToString());

        IEnumerable<DataRow> rows = dt.Rows.OfType<DataRow>();
        var result = from row in rows
                     group row by row[3] into callnumber
                     select new OnlineUserModel
                     {
                         Callednumber = callnumber.Key.ToString(),
                         Total = callnumber.Sum(p => Convert.ToInt32(p[2])),
                         Provinces = (
                         from pr in rows.Where(x=>x[3]==callnumber.Key)
                         group pr by pr[0]  into province 
                         select new ProvinceUser
                                        {
                                            ProvinceName = province.Key.ToString(),
                                            ProvinceCount = province.Sum(m => Convert.ToInt32(m[2])),
                                            Citys =
                                                       (
                                                         from pw in rows.Where(y=>y[0]==province.Key)
                                                         group pw by pw[1] into citys
                                                         select new CityUser 
                                                         {
                                                              CityName=citys.Key.ToString(),
                                                              CityCount=citys.Sum(n=>Convert.ToInt32(n[2]))

                                                         }


                                                        ).ToList()



                                        }
                                    ).ToList()


                     };

Code
{"Callednumber":"12590899766","Provinces":[{"Citys":[{"CityCount":5,"CityName":"北京"}],"ProvinceCount":5,"ProvinceName":"北京"},{"Citys":[{"CityCount":2,"CityName":"唐山"}],"ProvinceCount":6,"ProvinceName":"河北"}],"Total":11}