@Hope4cure Hi Yilin, and welcome to the JDRF TypeOneNation forum!
I’m certainly not surprised to read that the insulin dose your son has depended on for the last two years isn’t working now. The human body is a constantly changing, living organism which is constantly in a state of change - look back at how your body has changed over years/decades. As @Joe wrote, there are many more factors, other than meal-time [Insulin:Carbohydrate Ratio] insulin dosing that enter into effective diabetes management. A major factor could be your son’s age - many body changes are occurring. I suggest that you, your son and his medical provider look at your son’s total lifestyle - the BIG picture.
As I said, insulin needs fluctuate; me, for example. During the past 64 years living with insulin, my body had needed injected/infused as little as 15 units per day, and as much as 100+ units per day.