The National People's Congress (NPC) standing committee voted on the agreement in the closing meeting of its bimonthly session, state-owned news agency Xinhua said.
China is the largest shareholder in the AIIB, a multilateral development bank that aims to finance the construction of infrastructure across Asia.
The bank has 57 prospective founding members. Of these, 54 have signed an agreement to join, and the final three are expected to do so before the end of the year. All 57 countries will need to ratify the AIIB agreement before the end of 2016 to formally become founding members, according to Xinhua's report.
The AIIB was launched in Beijing last year to boost investment in infrastructure in Asia. It is expected to have initial capital of close to US$100 billion to invest in infrastructure projects. It will be financed by individual country contributions proportionate to their economic size.
The AIIB agreement only needs 10 signatory countries to approve legislation ratifying the agreement for the agreement to go ahead as long as their capital contributions make up at least 50% of the $100 billion total authorised capital earmarked for the Bank's initial operation, according to a UK government document (4-page / 249KB PDF).