Abstract: Based on the surface observational data,sounding data,monitoring data from automatic weather stations (AWS) and atmospheric constituent stations,an indicator that was established using parameters linking air-quality to meteorological condition (PLAM) was used to diagnose and predict the contribution of polluted meteorological conditions to aerosol pollution.An extremely heavy polluted event rarely occurred in Shenyang and the Songliao Plain in January 2017.The vertical structure of atmosphere as well as its effect on the increase in aerosol concentration, was studied in this polluted event,in order to investigate the influence mechanism of meteorological conditions on the formation of heavy air pollution in Shenyang.An index of the height of pollution mixing layer (H_PML) is defined in this study,which has significant meaning for the analysis and diagnoses of air pollution.The decrease in H_PML value favors the accumulation and increase in PM_2.5 concentration and vice versa.Based on the PLAM indicator and through the analysis of the atmospheric isentropic process,it is revealed that the atmospheric stratification can suppress the vertical dispersion and the H_PML value continues to decrease due to the feedback effect.The two-way belt of pollutant transport exists in the surrounding regions of Shenyang according to the indicator PLAM→_Shenyang,resulting in an obvious overlying effect on the air pollution in Shenyang,which is the crucial reason of this persistent and heavy pollution event.