Abstract: From August 24 to September 6, 2016, and 14 days before and after the implementation period of the guarantee measures of G20 Summit in Hangzhou were selected as the earlier and the later stages of the implementation of the guarantee measures, and the concentration changes of the main air pollutants in the guarantee area were analyzed. The WRF/SMOKE/CMAQ model was used to set up six scenarios of emission reduction for four types of pollution sources (industrial source, power plant source, dust source and road mobile source), and PM_2.5 and O₃ concentration changes were analyzed to evaluate the effect of strengthening environmental protection measures on air quality improvement. The results showed that: 1)During the whole research period, the concentrations of pollutants in Hangzhou were in the form of a wave, and the difference between the peak and valley concentrations of pollutants in most periods of the implementation of the guarantee measures was significantly smaller than that in the earlier and later periods; the average concentration of NO₂ was in the later period > the earlier period > the period of the implementation of the guarantee measures, and the effect of the guarantee measures on the emission reduction of NO₂ was significant; the concentration of O₃ in the period of the implementation of the guarantee measures was much higher than that in the earlier and later periods. 2)Compared with the same period in 2015, the concentrations of NO₂, SO₂, PM_2.5, CO and PM₁₀ in the core area and strict control area decreased during the implementation of the measures in 2016, with a decrease of core area > strict control area > control area; the concentrations of NO₂, PM_2.5, CO and PM₁₀ in the core area in 2016 were lower than those in 2017; the air quality in 2016 was better than that in 2015 and 2017; the impact of different control measures on air quality was different, and the variation of O₃ concentration was negatively correlated with the variation of other pollutants. 3)Four types of pollution sources were simulated to implement guarantee measures; the strong implementation of control measures in the core area and strict control area made PM_2.5 concentration decrease and O₃ concentration increase. 4)The simulation results showed that the control measures for industrial sources could effectively reduce PM_2.5 and O₃ emissions in the core area and strict control area; the control measures for power plant sources or dust sources could only slightly inhibit PM_2.5 and O₃ emissions in the core area and control area; the emission reduction measures for road mobile sources could significantly increase O₃ concentration in the core area and strict control area.