Abstract: Compared with the single-type air pollution, the formation and consumption mechanism of PM_2.5-O₃ combined pollution is more complex, with obvious spatial and temporal variabilities and diverse influencing factors in different regions of China. This study uses air quality data from 302 cities across 8 regions (Northeast China, North China, East China, South China, Central China, the Loess Plateau, the Sichuan Basin, and the Tibetan Plateau) to investigate the temporal evolution and regional differences of the PM_2.5-O₃ combined pollution from 2015 to 2024. The research results show that: (1) Implementation of air pollution control policies has led to an 82.5% reduction in the regional average number of days with PM_2.5-O₃ combined pollution during 2019-2024 compared with 2015-2018. (2) There is a clear correlation between regional economic development and PM_2.5-O₃ combined pollution days. After 2018, more economically developed regions such as North and East China experienced, on average, three to five more PM_2.5-O₃ combined pollution days per year than the less developed Sichuan Basin and Loess Plateau. (3) High-latitude regions show peak PM_2.5-O₃ combined pollution in spring, whereas in low-latitude regions, autumn is the predominant season for such events. (4) In South China, the combination of lower latitude and relatively warm winters favors O₃ formation, resulting in frequent wintertime PM_2.5-O₃ combined pollution. The research indicates that the number of summertime PM_2.5-O₃ combined pollution days has significantly decreased across various regions of China in recent years. However, PM_2.5-O₃ combined pollution events continue to occur during spring and autumn in North and East China. To effectively mitigate this issue, region-specific control strategies targeting PM_2.5 and O₃ during transitional seasons should be further strengthened.