The Party Central Committee and the State Council attach great importance to the prevention and control of air pollution, and will win the battle to defend the blue sky as the top priority in fighting the pollution. In recent years, China's ambient air quality has continued to improve, and the concentration of fine particulate matter (PM2.5) has fallen sharply, but the effect of improving ambient air quality has not been stable. During the autumn and winter of the Yangtze River Delta, the atmospheric environment is still severe, and the average PM2.5 concentration is 1.8 times that of other seasons. In the autumn and winter of 2018-2019, 10 cities in the Yangtze River Delta region did not complete the PM2.5 concentration reduction target. Among them, 5 cities increased without falling year-on-year, and the spatial distribution characteristics of PM2.5 concentration “high in the north and low in the south” are still obvious. 2020 is the target year and key year for the three-year action plan to win the Blue Sky Defense War. The success of the autumn and winter of 2019-2020 will directly affect the achievement of the 2020 target. According to forecasts, due to the influence of El Niño, the overall deviation of meteorological conditions in the autumn and winter of 2019-2020 is not conducive to the spread of atmospheric pollutants, further increasing the pressure on air pollution control, and greater efforts and more practical measures must be taken to offset the adverse weather conditions Negative effects. All localities must fully understand the importance and urgency of comprehensive air pollution control in the autumn and winter of 2019-2020, solidly advance various tasks and measures, and lay a solid foundation for resolutely winning the defense of the blue sky and building a well-off society in an all-round way.