* You need to follow Hague Process
The state department has this page for adopting relative child:
http://adoption.state.gov/adoption_process/who_can_adopt/relatives.php
China and US is parties to Hague International Adoption Convention, therefore you need to follow Hague Process. http://adoption.state.gov/hague_convention/countries.php
See more detail here
http://adoption.state.gov/hague_convention/overview.php
There are two other process for adoption, www.uscis.gov/adoption/immigration-through-adoption but neither of them suits your purpose, for completeness of reference, I list them below
* Orphan Process: the child must be orphan...
* Immediate Relative Process: the child must already be adopted in a foreign country and the US citizen must be legal guardian of the child, and lived with the child for two years (in the foreign country).
As you can see neither process suits you, and you can only try Hague Process.