Abstract: For exploring the source of PM_2.5 of Nantong in 2020, the characteristics, correlation and industrial contribution of chemical components of PM_2.5, and the internal and external seasonal contribution of PM_2.5 were analyzed based on the high time resolution observation data of super stations. At the same time, WRF-CMAQ model was used to construct meteorological field and pollutant field for the simulation of the ambient air quality of Nantong in January, April, July and October of 2020. The results show that the secondary inorganic ion is the main component of PM_2.5 in Nantong City, and their concentrations have obvious seasonal difference. The sharp increase of nitrate concentration is an important reason for the aggravation of PM_2.5 pollution in Nantong city. The aggravation of PM_2.5 pollution level in winter was affected mainly by vehicle exhaust emission. From the perspective of 2020 as a whole, according to different meteorological conditions and pollution types in different seasons, the proportions of the pollution sources were also different. The local emission contribution of PM_2.5 in Nantong is about 61%, followed by long-distance transmission from the north (17%), and from the Yangtze River Delta and southern Jiangsu (18%). The verification on the simulation of all pollutants in the air quality model can well represent the change trend of pollutants. Although, there is a certain gap between the simulated value and the observed value, it is still within a reasonable and acceptable range. The results worked out by the model are reliable and can be used in subsequent researches.