我參考這篇https://frank1025.pixnet.net/blog/post/350482198-%5Basp.net-c%23%5D-014-%7C-%E5%89%8D%E7%AB%AF%E9%80%8F%E9%81%8Eashx%E9%A0%81%E9%9D%A2%E8%BF%94%E5%9B%9Ejson%E8%B3%87%E6%96%99
但是不知道為何回傳的格式變成string

        $.ajax({
            type: "GET",
            url: url,
            data: {},
            contentType: "application/json; charset=utf-8",
            dataType: "JSON",
            success: function (data) {
                var obj = data.d;
                console.log(obj);
            }
        });

後端

        [WebMethod]
        [ScriptMethod(UseHttpGet = true)]
        public static string GetData(string group)
        {
            
            SQLDB db = new SQLDB();
            string time_s = "2021-10-15 00:00:00.000";
            string time_e = "2021-10-15 02:00:00.000";
            List<List<string>> par_list = new List<List<string>>();
            par_list.Add(new List<string>() { "{ min:'" + time_s + "'}" });
            par_list.Add(new List<string>() { "{ max:'" + time_e + "'}" });

            string sql = "DECLARE @STime Datetime DECLARE @ETime Datetime DECLARE @FactoryID nvarchar(10) DECLARE @TagName nvarchar(50) " +
                "set @STime = '2021-10-15 00:00:00.000' set @ETime = '2021-10-18 00:00:00.000' set @FactoryID = 'KY-T1HIST' set @TagName = 'HPA-5_KW' " +
                "exec h_GetTagValuelist @STime ,@ETime ,@FactoryID ,@TagName";
            DataTable dt = db.GetDataTable(sql, CommandType.Text);
            string d = "";
            for (int i = 0; i < dt.Rows.Count; i++)
            {
                string datatime = Convert.ToDateTime(dt.Rows[i][0].ToString()).ToString("yyyy-MM-dd HH:mm:00");
                string v = dt.Rows[i][2].ToString();
                Decimal z = 0;
                if (v.Length > 0)
                {
                    z = Convert.ToDecimal(v);
                    if (z > 0)
                    {
                        d += "{x:" + "'" + datatime + "'" + ",y:" + z + "\"},";
                    }
                }
                //int z = Convert.ToInt32(x);
                //d += "{x:" + "'" + datatime + "'" + ",y:" + z + "\"},";
            }
            par_list.Add(new List<string>() { d });
            //轉換為JSON
            System.Web.Script.Serialization.JavaScriptSerializer o = new System.Web.Script.Serialization.JavaScriptSerializer();
            string datas = o.Serialize(par_list);

            //修改格式
            datas = datas.Replace("\\", "");
            datas = datas.Replace("\"", "");
            datas = datas.Replace("u0027", "'");
            return datas;

            
        }