Abstract: In order to reveal the evolution characteristics of compound air pollution, spatiotemporal characteristics of PM_2.5 and O₃, as well as their correlation relationships and the formation mechanism of the synergistic effect, were comprehensively analyzed based on the monitoring data in 17 cities in Hubei Province from 2015 to 2020 and the atmospheric superstation in Wuhan. The results indicated: (1) PM_2.5 pollution was significantly mitigated with a decline rate of 4.7 μg/(m³·a), and O₃ pollution worsened with a growth rate of 3.8 μg/(m³·a) and it appeared frequently in the warm season (April to October). In addition, PM_2.5 concentration in winter was still high, especially in central cities. The number of days with O₃ exceeding the standard in eastern cities was the same to the number of days with PM_2.5 exceeding the standard in the past two years. (2) The PM_2.5 and O₃ in Hubei Province had an increasingly close relationship, and the synergistic effect was significant. The daily values showed that PM_2.5 and O₃ had a significant positive correlation in summer (the correlation coefficient (R) is 0.57), and R was as high as 0.63 when PM_2.5 ≤ 50 μg/m³ in the past two years. In addition, there was a positive correlation between PM_2.5 and O_x in winter, with the highest in eastern cities in 2020 (0.46), showing the importance of atmospheric oxidation for the secondary pollution of PM_2.5. (3) The causes of the synergistic effect of PM_2.5 and O₃ in Wuhan were as follows. In the warm season, the intensified O₃ photochemical reaction was controlled by VOCs due to high temperature, moderate humidity, weak wind and the high emissions of precursors (VOCs and NO_x) under the background of low PM_2.5, which will cause O₃ pollution, thereby enhancing the secondary transformation of PM_2.5. In winter, high atmospheric oxidation and unfavorable weather conditions promoted secondary aerosol transformation. During the heavy pollution episodes, PM_2.5 components were mainly secondary inorganic components such as nitrate. (4) The coordinated control in Hubei Province is mainly to strengthen the control of VOCs on the basis of maintaining NO_x control, suppress the rise of O₃ concentration in warm season, especially in the eastern region, and enhance the control of PM_2.5 in winter, especially in the central region.