To control the novel coronavirus disease (COVID-19) outbreak, China undertook stringent traffic restrictions and self-quarantine measures. We herein examine the change in air pollution levels and the potentially avoided cause-specific mortality during this massive population quarantine episode. We found that, due to the quarantine, NO2 dropped by 22.8 μg/m3 and 12.9 μg/m3 in Wuhan and China, respectively. PM2.5 dropped by 1.4 μg/m3 in Wuhan but decreased by 18.9 μg/m3 across 367 cities. Our findings show that interventions to contain the COVID-19 outbreak led to air quality improvements that brought health benefits which outnumbered the confirmed deaths due to COVID-19 in China