A Chinese citizen marries an American. They apply for a Green Card after marriage. It is issued. How often do they have to go to United States and how long a time per year do they need to live in US. To maintain green card.

Six months...

They should return to the US every 6 months, and try to stay in the US as long as possible. They should also have as many ties to the US as possible. File taxes, maintain a residence, car, drivers license, bank accounts, credit cards, physicians, insurance, etc.