According to the General Principles of the Civil Law of China, if both partners are foreigners, you can register your marriage at the registration office in the city where you both live. Generally speaking, at least one of you must reside in China.
you both should back to your own country for the certificate of marriageability, sames as a single status certificate, signed and notarized by both related US and Chinese authority. Application requirements may vary from office to office, so, you'd better visit your local registration office in China before back to US.