Abstract: Based on the predicted data of Chinese population from 2016 to 2100 from the United Nations, this paper takes such factors as ageing, urbanization and population mobility to measure the scale and the age structure of China’s urban and rural population and the characteristics of the population who have ensured in the Urban Basic Endowment Insurance Scheme and the Urban and Rural Residents Social Endowment Insurance Scheme. On the basis of this, it constructs an actuarial model for the sustainability of pension insurance funds. The results show that even though the pension insurance system is under the multi-parameter synchronization adjustment and reform, the Urban Basic Endowment Insurance Scheme will still bear a debt of RMB 21.91 trillion during the observation period, while the Urban and Rural Residents Social Endowment Insurance Scheme will accumulate a balance of RMB 5.62 trillion with the massive fiscal subsidy. Therefore, the enlightenment includes that it is in urgent need to study and carry out the marginal reforms of the pension insurance systems and give full play to the comprehensive effects of the multi-parameter synchronization adjustment. Besides, we should seek various fund sources beyond the system, narrow the gap between employees and residents through increasing the personal payment of the urban and rural residents, and increase the coverage of the rural migrant workers in the Urban Basic Endowment Insurance Scheme, so as to improve the institutional equity.

Key words: ageing; population mobility; pension insurance fund; sustainability; marginal reform