The U.S. taxes “U.S. taxpayers” on their world-wide income, unless it is overridden by a bilateral treaty that is on point. A “U.S. taxpayer” is either a U.S. citizen or a U.S. resident alien. This means that an individuals who hold a U.S. permanent resident card (or green card) but live in a foreign country, like China, will be subject to U.S. income tax on all their income—even if it were earned in that foreign country.