What's the use of a green card

Upstairs is wrong. A green card is permanent residence. You are still a national of China. A green card means the right to live permanently in this country. Enjoy the same economic rights and obligations as citizens, but have no political rights. The green card is also a preparatory stage for becoming a citizen of the country. Generally, you can apply for naturalization and become a citizen by holding a green card for a certain number of years (3-5 years). In order to maintain the green card status, you must live in the country where the green card is issued, otherwise the green card will be revoked because of insufficient immigration tendency.