Compound heatwave and ozone pollution events threaten public health as warming and photochemistry intensify. Yet the internal architecture of these events—how heatwaves and ozone separately influence frequency versus intensity—remains poorly resolved at national scale. Here we show, using 1 km resolution grids across China from 2000 to 2023, that heatwaves dominate the frequency of compound extremes while ozone dominates their intensity, and that this asymmetry strengthened after 2016. Population exposure rose primarily because the events themselves intensified, rather than from population growth. City-level influencing factors proved highly heterogeneous, reflecting local combinations of meteorology, pollution and socioeconomic conditions. These findings uncover an asymmetric architecture of compound risk and identify distinct levers—heat versus ozone—for targeted mitigation under continued warming.