Capital gain is taxed at a much lower rate, I think it's 15% instead of 25% or more for a middle-class income.
In your case, your capital gain is 380 wan yuan, but maybe not all of them are subject to US tax.
(1) Your argument could be that your world wide property is subject to US tax only when you became a green card holder in 2009. Therefore, all the capital gains made from 1996 to 2009 are not subject to US tax, and only the capital gains from 2009 to now should be taxed.
(2) How to determine the equivaluent US dollar amount for the 380 wan yuan. The exchange rate fluctuate all the time and as you said, you might not exchange them back to US dollar this year or even next few years.
You need to consult a tax expert for above two questions.