Abstract: Understanding and mastering the population changes during the 14th Five-Year Plan period is of great reference value to the implementation of China's social and economic policies. This paper predicts the population size and structural changes during the 14th Five-Year Plan period, and summarizes the four transitions. The total population keeps increasing, the growth rate of the elderly population accelerates, and the average annual death population continues to increase, but the working age population, children, female population of childbearing age and average annual birth continue to decline. From the perspective of population structure change, the proportion of children and working age population both decreases, the proportion of elderly continues to increase, and the driving of population aging change from bottom to top, the dependency ratio remains low, but the imbalance of gender ratio is transmitted to the marriageable age group. The major transition of population will have a profound impact on social and economic development, including the coming negative growth of population, the acceleration of aging process, the interweaving of marriage and childbearing concepts, and the quality and quantity changes of labor force. In order to cope with population changes, strategic measures must be carried out from reproductive rights, pension security, economic transformation and social system.