In the late 1970 of the 20th century, China began to shift from the traditional planned economy to market economy, which undertook a series of system innovations during the process of economic restructuring. In the context of economic restructuring and the ageing of the population, old-age insurance system in China also carried out a range of system innovations. From the perspective of institutional innovation, this article studies the innovation process from pay-as-you-go system to the current combination model of social poling and individual accounts, the creative mode of which appears a system imbalance, for example, low level of pension plan as a whole, empty account operation of individual account and large evaluation risk of fund and so on. Due to the system of innovation is a dynamic process, so the author considers that the future old-age insurance system should be further institutional innovation and implementation of the "nominal accounts" system, in order to better bridge the insufficient combination model of social poling and individual accounts, which makes China's endowment insurance system more effective.