My girlfriend's parents constantly makes me pay for meals when we eat together. They know that I'm well to do, and I know they are not. Am I just being petty?

If they're doing that when she's only your girlfriend, imagine what they'd be like as in-laws. You might want to float the idea of "going Dutch" and splitting the bill. The "keepers" tend to insist (or at least offer) to pay their share.

Are your parents there too? Maybe the his parents can tell her parents if they only listen to 同辈.

Being generous is okay, but not being taken advantage of. The fact that you would ask means you feel like you are being taken advantage of. Talk to your gf and let her know. See if she wants to come up with a solution with you. (One way is saw people resolve, is for the girl to give money beforehand to the guy, before the guy pays for the meal. )

Actually if u can afford i dun see the problem. What exactly is the concern here?

I think it is fair to go Dutch.

You can always declare the per pax cost on the spot and get everyone to pay their share.

You can be generous to them and give a treat from time to time but it should not be a case where everyone keeps quiet and you become the default person to pay.