Where should I buy my pc parts if I live in shanghai China?

So you are forced to buy from the United States, not locally?

If so you can use PCPARTPICKER which also is useful to "build" a PC as it can help avoid parts that are not compatible.
http://pcpartpicker.com/

It links to various online stores like Amazon, Newegg etc.
 
Well local stores are always the best, if you find any in Shanghai. If you can get order from Newegg that would be the safest option (if they ship to China.)