Contact the US Consulate in China. See this statement at :
http://www.uscis.gov/portal/site/uscis/menuitem.eb1d4c2a3e5b9ac89243c6a7543f6d1a/?vgnextchannel=8ae33a4107083210VgnVCM100000082ca60aRCRD
How to Renew a Green Card If You Are Outside the United States
If you are outside the United States and your green card will expire within 6 months (but you will return within 1 year of your departure from the United States and before the card expires), you should file for your renewal card as soon as you return to the United States.
If you are outside of the United States when the card expires and you have not applied for the renewal card prior to your departure, you should contact the nearest U.S. Consulate, USCIS office, or U.S. port of entry before attempting to file Form I-90 for a renewal green card.
For more information, read this link:
http://www.saculbreathlaw.com/blog/?p=499
