There are three aspects in the financing mechanism of pension insurance in China, namely, the "combined accounting system" in regulatory documents, the "complete fund system" in substantive norms and the "pay-as-you-go system" in actual operation, showing the huge gap between norms and facts of financing mechanism of China's pension insurance, which greatly hinders the effective operation of the system. The pension insurance system should promote the institutional purpose of labor-management cooperation and social solidarity, which determines the "combined accounting system" distinguishing between individual accounts and pooling accounts, and that employers bear most of the pension insurance rates. It is very debatable. Although the pay-as-you-go system will show a relatively rapid failure to pay in the face of population ageing, due to the essential requirements of the mutual supportive community, the pension insurance financing mechanism should also abide by the "insurance principle" to ensure that the funds are earmarked, in order to make the pension fund be far away from the uncertainty of the capital market, ensure the stability of the pension income and expenditure, reduce the political and economic risks of the government, and avoid the abduction of the state by the capital monopoly. So the pay-as-you-go system is more preferable than the fund system. Fully drawing on the beneficial experience of foreign countries and combining with China's specific national conditions, in the future, China's pension insurance financing mechanism should consider abolishing the "personal account" and implementing the current balance of pension insurance income and expenditure to realize pay-as-you-go under the single account system.