The prevention and control measures in place during the coronavirus disease 2019 (COVID-19) pandemic served as perfect conditions for a natural experiment, which has provided an opportunity to investigate the extent to which environmental regulations can improve air quality in the short term. This article examines the relationship between anti-epidemic measures and air quality via a regression discontinuity design (RDD) based on the daily data from 326 prefecture-level cities in China. The empirical results indicate that, during the period of epidemic prevention and control in China, the air quality index (AQI) significantly decreased by 20.56, and the emission concentrations of the pollutants PM_2.5, PM₁₀, and NO₂ decreased by 19.01, 20.20, and 2.13, respectively. It was further found that the continued operation of life-supporting industries during the epidemic, such as thermal power plants and heating industries, may be the reasons why there were no significant decreases in the concentrations of SO₂ and CO. The O₃ concentration, which is related to sunlight and the concentrations of NOx, was also not found to have changed significantly in the short term. Moreover, it was found that the more daily confirmed COVID-19 cases in an area, the greater the improvement of the air quality.