5 million American green cards immigrated to China.

The topic asks, "Children studying in the fifth grade of primary school in China and studying in the United States in the second grade of junior high school can go back to China to study in the United States?" You can't.

Because the child holds an American green card, which means an American permanent resident card, the time for returning to China cannot exceed 1 year. According to American immigration law, permanent residents must use a valid immigrant visa and a valid home country passport when entering the United States, otherwise green card holders cannot leave the United States for more than 40 days at a time. Returning to China with an American green card will not be restricted because you are a citizen of China. However, in order to maintain the validity of the green card, you can return to China for up to six months, and then you must return to the United States. Otherwise, the US Immigration Service will wonder if you really want to become a permanent resident of the United States.