Abstract: Purpose/Significance Reasonable environmental policy tools are the important basis for sustainable development. Design/Methodology In this paper, the Differences-in-Differences (DID) and the Propensity Score Matching-Differences-in-Differences (PSM-DID) based on the propensity score matching are used to analyze the impact of the command-controlled environmental policy on the air quality before the “G20 Summit” held in Hangzhou in 2016. Conclusions/Findings (1) The long-term policy has effectively improved air quality, and its effect is obviously better than the short-term policy, which guarantees the excellent quality of the air in Hangzhou before and after the “G20 Summit”. (2) The blue sky created by long-term policy is stable and continuous. There is no big fluctuation or rebound in air quality before and after the “G20 Summit”. (3) The long-term policy of the “G20 Summit” has a long-term effect. The air quality has been maintained at a good level for a long time, and there is no deterioration. The results of this paper are still robust after considering common trends, different forms of pollutants, changing different samples, and selecting different models.