The country is the world's largest emitter of harmful CO2 emissions, which cause climate change.
China and the US are expected to jointly announce ratification at a bilateral summit later on Saturday.
In a landmark deal struck in December, countries agreed to cut emissions enough to keep the global average rise in temperatures below 2C (36F).
Members of China's National People's Congress Standing Committee adopted "the proposal to review and ratify the Paris Agreement" on Saturday morning at the end of a week-long session.
The Paris deal is the world's first comprehensive climate agreement. It will only come into force legally after it is ratified by at least 55 countries, which between them produce 55% of global carbon emissions.