public class UserInfo
{
  [JsonProperty("id")]
  public int Id{ set; get; }
  [JsonProperty("userName")]
  public string UserName{ set; get; }
}

var user = new { Name = "john", Age = 19 }; 
 var serializerSettings = new JsonSerializerSettings
      {
        // 設(shè)置為駝峰命名
        ContractResolver = new CamelCasePropertyNamesContractResolver()
      };
var userStr = JsonConvert.SerializeObject(user, Formatting.None, serializerSettings);