My son and I both have Chinese passports and green cards. My son's passport expires in January. I

You son can get his passport renewed in US from the consulate. Make sure apply in person with following documents:
1. Application form for Chinese passport renewal.
2. 4 passport-sized photo;
3. Original passport and copies of information page, extension page, US visa page, pages of exit China record and enter US record.
4. Original and copy of US green card.
The processing takes about one month.