PM_2.5 and O₃ are the most important air pollutants in Fangchenggang City, and the air pollution days are mainly occurred in autumn and winter. According to 500 hPa circulation pattern, air pollution can be divided into northwest air flow pattern, westerly air flow pattern and southwest air flow pattern, and according to the surface pressure field, it can be divided into the cold high-pressure ridge type, uniform pressure field type, high pressure rear and low pressure front type. In the absence of overseas input, PM_2.5 is produced in the weather environment with low wind speed, low temperature, low visibility, high humidity and no rainfall or no obvious rainfall, while O₃ is produced in the weather environment with high temperature, low humidity, sufficient sunshine, high wind speed and good visibility. In terms of vertical movement, the downdraft in the middle and low levels is conducive to the accumulation of air pollutants. In terms of temperature stratification distribution, the inversion layer at 700~850 hPa is very important for the increase of PM_2.5 concentration. The effect of inversion layer near the ground on the increase of PM_2.5 concentration is weaker than that of the low layer. The inversion layer near the ground is very important for the increase of O₃ concentration, but the inversion layer at the low layer is not important.