Xiaobaitu and Others about Customs Declaration U.S. to China, Ch

Dear Xiaobaitu and Others,

I have some questions regarding the customs declaration for a trip to China and hope to have the answers to them.

1. While leaving U.S., do I need to file customs declaration form? If yes, at check-in counter at the airport or on board?
2. While leaving China, do I need to file customs declaration form?
If yes, at check-in counter at the airport or on board?

Thanks.