As far as I am aware quad bikes are not road legal in China. This is because they have no license category. I have seen them ridden on road illegally, and I wouldn't bother unless it was a seriously rural area. Silly covered four wheel vehicles with scooter engines and 3 wheelers are legal in some areas and others as 'old people cars' with special registration some with normal yellow motorcycle 'lower form of life' plates.

I know it's a silly rule. In China color-blind people are banned from driving, but I've heard of one-eyed and colorblind international airline pilots...go figure. Obviously quads are fun, and any bureaucrat would be against that on principal.