My passport has expired in America. Can I go back to China? Can I buy a round-trip ticket?

I guess you mean that your China passport and American visa have expired.

There is no problem in returning to China after the visa expires. As long as you have not overstayed, the US Immigration Service will not embarrass you when you leave the country. If the passport expires, there will be problems in leaving the United States, connecting flights and entering the country.

There is not much problem in buying a plane ticket. General travel agencies only require your name and passport to be the same.

It is recommended to apply for a new passport at the China Embassy or Consulate in the United States where you live. If you return to China for a short time, you can apply for a China citizen travel permit first, and then apply for a new passport after you return to China.