Abstract: Based on the meteorological observational data and PM_2.5 concentration monitoring data in Chaoyang District,Beijing from 2011 to 2015,weather types during heavy air pollution were analyzed.The results show that three weather types can be generally identified under heavy pollution conditions,i.e.,uniform pressure field,low pressure with convergence,and high pressure.For uniform pressure field type when heavy air pollution occurs,atmospheric stratification is stable and surface wind speed is weak,which results in the accumulation of pollutants at a low level.Meanwhile,due to the local topography effect,the mountain-valley wind circulation becomes significant over the Chaoyang District.The weather type of low pressure with convergence is characterized by ascending motion in the front of the trough,which leads to the accumulation of pollutants in the center of low pressure and the formation of heavy air pollution.Under high-pressure type,Chaoyang District locates in the rear or bottom of surface high pressure and is influenced by the southerly or easterly flows,and then pollutant concentration increased due to strong regional pollutant transport.On the whole,when three weather types appear alternately,persistent and heavy pollution easily occurs in Chaoyang District.