using Newtonsoft.Json;

namespace WebApi.Controllers

{

    public class Rootobject

    {

        public string PhoneNumber { get; set; }

        public string Name { get; set; }

        public string MF { get; set; }

        public string BirthDate { get; set; }

        public object MaritalStatus { get; set; }

        public object Country { get; set; }

    }

    [Route("api/[controller]/[action]")]

        [ApiController]

        public class ValuesController : ControllerBase

        {

            [HttpGet]

            public IEnumerable<string> Get()

            {

                var jsonSetting = new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore };

                var data = new Rootobject() {PhoneNumber="13800138000", Name="测试" };

                var json = JsonConvert.SerializeObject(data, Formatting.Indented,jsonSetting);

               return new string[] { json };

            }

    }

}

//结果:
{
  "PhoneNumber": "13800138000",
  "Name": "测试"
}