Population flow can influence the growth of regional carbon emissions. This paper analyzes the dual transmission mechanism of population flow’s impact on population structure and carbon emission. On this basis, it empirically studies the impact of population flow and other related factors on carbon emissions in China by using panel data of 30 provinces and cities in China from 2005 to 2018 with panel econometric regression and heterogeneity analysis. The results show that, i) Over all, no matter in long-term or short-term, China’s population flow can reduce the growth of carbon emissions. ii) The aging of regional population and knowledge structure improvement caused by population flow helps reduce carbon emissions, while the regional urbanization caused by population flow and household miniaturization have no significant correlation with the growth of carbon emissions. iii) From the perspective of geographical heterogeneity, the northwest of "Hu Huangyong line" has poor ecological environment, low population density and low level of economic development. Population flow promotes the increase of carbon emissions, while the southeast of "Hu Huangyong line" is on the contrary. iv) The consumption level of Chinese residents, per capita GDP, energy intensity and energy consumption structure have positive effects on carbon emissions, while carbon emission intensity has negative effects. Finally, this paper puts forward relevant suggestions from the perspective of coordinating population policy and energy conservation and carbon emissions reduction policy.