Abstract: In order to understand the influence of winter local circulation on the spatial and temporal distribution of air pollution in Chengdu, hourly PM_2.5 concentration data and ERA5 reanalysis data of Chengdu Environmental Monitoring Station in January 2018 were used to analyze the local circulation variation and its influence on PM_2.5 concentration distribution during a heavy pollution process in January 2018. The results show that the local atmospheric circulation played an important role in the regional transmission and diffusion of pollution, especially in the beginning and maintenance stages of pollution, which was mainly affected by the valley wind circulation. The valley wind in the morning and evening changed in the western part of Chengdu and formed wind field convergence, which aggravated the local air pollution, while the enhancement of valley wind and ascending motion from noon to afternoon alleviated the air pollution from east to west. The transportation and convergence of the valley wind in winter made the atmospheric pollutants continuously circulate and accumulate in a daily cycle, which played an important role in the formation of heavy air pollution in the western region of Chengdu.