autumn > spring > summer. The occurrence frequency of the temperature inversion in winter in Harbin is significantly higher than that in summer, autumn and winter. The concentration of air pollutants in Harbin was, in the recent 4 years, positively correlated with the with the frequency and the thickness of the continuous inversion, and positively correlated with the inversion intensity at 07:00, and the correlation with the intensity at 19:00 was not obvious, indicating that the lowlevel atmospheric inversion in Harbin is one of the main factors affecting the air quality of Harbin. The weak cold advection at high latitudes, the warm lower layer, the weak air pressure field at the sea level, and the poor horizontal and the vertical transportation made the pollutants difficult to spread and accumulate, which is the important cause of the severe pollution in the last few days."/>