Can't go to America without an American green card? Get married and have children in America?

A green card means legal permanent residence. With a green card, you can live for a long time (unless you do something illegal, you may be deported), and the validity period of the green card is 10 years (it will be replaced after 10 years). There are many ways to get a green card. Marry a person with American nationality, or American students can find a job in the United States after graduation. Or what "bad things" you did in China. If you are eligible to apply for political asylum and immigration (which is usually difficult), you can stay in the United States as long as you don't break the law and don't get caught by the police. However, this job and life are just some jobs in China. You can't work in foreign companies and institutions because they are very strict. You haven't been caught with any evidence. If the police send you to the immigration office, you may be deported because you are an illegal immigrant or an illegal immigrant.