-Because the adopting parent has been a US citizen when adopting the child, and China and US are the Hague Convention countries, the adoption has to follow the Hague Convention Adoption rule. The adoption has to be completed based on both Chinese adoption law and US adoption law, following certain processes. The procedure is somewhat completed, so had better hire an immigration lawyer.
The previous adoption through the US local court will not be accepted by USCIS for the immigration benefit.
Here are some links for your information:
http://www.uscis.gov/adoption/immigration-through-adoption/hague-process
http://www.hooyou.com/adoption/hague.html