Ambient PM2.5 (fine particulate matter) pollution in China has been greatly reduced in recent years, especially since the implementation of the Clean Air Action in 2013. The analysis of variations in the pollution-related health burden and its driving factors has important implications for policy makers in terms of further improving the health benefits associated with air pollution control. Here, the Global Estimates Mortality Model was adopted to newly estimate the annual mortality attributable to PM2.5 in China from 2004 to 2017. Then, the effects of the changed ambient PM2.5 concentrations, population size and migration, aging and baseline mortality rate on the total variation of the PM2.5 health burden were quantified, and insights were provided into the factors impeding the achievement of health benefits as air pollution is mitigated. Our modelling results showed that the national PM2.5 health burden generally increased from 2.22 million (95% confidence interval: 1.39–2.98) in 2004 to 2.45 million (1.72–3.13) in 2017 with a tendency to rise first and then decline, and peaking at 2.65 million (1.60–3.60) in 2013. The average exposure to ambient PM2.5 in China has dropped since 2011, two years earlier than the overall PM2.5-attributable mortality turning point. Compared to 2013, the mitigation of PM2.5 pollution would have prevented 0.85 million deaths in 2017, at the same time, the effect of the population aging determined the addition of 0.51 million deaths from air pollution, which partly masked the effect of the mitigation. For future air pollution control policies to alleviate the public health burdens in the fast-growing Chinese cities, attention should be focused on old age care, especially in areas where PM2.5-attributable mortality may increase.