The assessment of environmental and health impacts stemming from sports mega-events plays an important role in evaluating the overall cost–benefit of the events. This study utilizes microdata sourced from the China Household Income Project in conjunction with a time-varying difference-in-differences methodology. Through this approach, we estimated the impact of the 2010 Guangzhou Asian Games on both air quality and public health conditions within China. The results reveal the following: (1) The Games wield substantial and favorable effects on self-perceived health; (2) The primary avenue through which the Games improve self-perceived health is by mitigating air pollution levels in the cities associated with the Games; (3) The cost–benefit analysis unveils that hosting the Games has led to a reduction of 1103.12 million RMB in residents’ medical expenses, with the improved air quality accounting for 20.15% of the cost reduction.