Abstract: Different from developed countries, China′s population structure in the middle-income stage is characterized by “aging and fewer children”.Based on the panel data of China′s regions from 1992 to 2017, this paper uses the extended MRW model to analyze the impact of the double superposition of “aging” and “fewer children” on economic efficiency.The results show that the comprehensive influence of “aging and fewer children” on China′s economic efficiency is negative, and the population structure of “aging and fewer children” has a negative impact on China′s transformation of economic development mode and economic growth power, which is not conducive to the continuation of China′s transformation from material capital driven to human capital driven in per capita GDP level, and promotes the premature emergence of supply side structure deceleration in China′s economy. The logic to promote the smooth transformation of China′s economy should be to first improve the income level, then transform the driving factors; during the transitional period, maintain the original economic growth momentum, ensure the per capita income level to enter the ranks of high-income countries; moderately carry out the accumulation of material capital, encourage childbearing and improve the per capita human capital accumulation level, improve the per capita human capital stock, and make it continuously increase speed, so as to realize the smooth transition and handover of two kinds of power.

Key words: Key words：demographic transition;aging and few children, economic efficiency, economic restructuring