If your income exceeds $4100 a year, you earn maxium 4 credits for the year. You need total 40 credits to qualify for Social Security benefits. That is where you need at least work for 10 years to qualify. Once you qualify for the benefits, you can get them in China if you decide to go back. But if you only contribute 10 years to your social security tax, do not expect get much after you turn 65.