Do I need to reactivate my Chinese SIM card if I haven't used it for a year?

It still can be used and no need to reactivate. However, as you haven't used it for a year, there should be arrearage of your sim card and it may be much money. I suggest you check the arrearage first. If it is not taht much, just pay off them at a relevant office and use it again. If it will cost you much, it would be better to get a new SIM card!