Need help:

Need Help: We got divorced in New York City, my son was born in China and is under the cust of my ex-wife who got married. My ex-wife said she does not have a job recently. My son is still in China and he has never been to US. How much should I pay, should I pay according to the living standard of US or of China. Someone told me I should pay according to China's living standard, but I just cann't find which item of the law this is up to. Thanks.