Ming dynasty saw the introduction of sweet potato,corn,potato and other American food crops into China,among which sweet potato was widely spread in China due to its advantages of high yield and easy cultivation and had become one of the staple crops in the late Qing dynasty.The introduction of sweet potato made an important contribution to the development of Ming and Qing dynasties,especially the growth of population.This research collected data about the the time of introducing sweet potatoes into each province,planting situation,land suitability and the relevant data such as population from chronicles of 17 provinces and other historical data.Then the method of difference-in-difference (DID) was applied to conduct a quantitative study on the impact of sweet potatoes on population growth in the Ming and Qing dynasties under the control of important covariates including the time of introducing corn,war,disaster,infectious diseases.The results showed that the introduction of sweet potato had a significant positive effect on the growth of population,and this effect in the south was much greater than that in the north.