Abstract This paper puts the population, economy and pension into a unified framework, analyzes the interactive feedback mechanism between them, and builds a system dynamics model to explore the moderate scale of China’s pension strategic reserve from the following three perspectives: whether it can resist the pension payment crisis in future according to the current growth rate; if the pension gap is completely filled by the reserve, what size of the reserve needs to reach; a moderate range of the reserve when local governments are jointly responsible for filling the gap. The empirical research shows: the reserve cannot resist the pension payment crisis; the reserve needs to reach 54.21 trillion RMB before the gap appears, under the condition of fully filling the gap; the reserve needs to reach the range of 19.96 trillion to 39.51 trillion RMB before the gap appears with the participation of local governments.