Induced by numerous environmental and anthropogenic factors, the frequency of compound hot extremes (CoHot) is increasing globally. However, there is a lack of a comprehensive understanding of the relative importance of different factors in the change of CoHot, as most studies focused solely on individual factors. We systematically attribute the long-term trends of summertime CoHot in China to 24 factors including climate background, climate change, urbanization (including impervious area expansion and three-dimensional urban morphology), and vegetation change, using partial least square regression (PLSR) and variable importance projections for analysis. Cross-evaluation results based on 2259 meteorological stations indicate that the PLSR model accurately simulates the trends of CoHot frequency, duration, and intensity, with a relative error of 4–20% from national to individual station scales. A warm and humid climate background, rising average summertime temperatures, impervious area expansions, high building volume densities, low building heights, and vegetation wilting are the main factors that favoring the increasing and intensifying trends of CoHot. Although summertime warming contributes the most, the significance of urbanization and vegetation greening has been growing in recent years. Urbanization's contribution increases from 9.3% on a national scale to over 40% in urban centers, mainly due to increased building volume density rather than expansions of impervious area. In northern China, vegetation greening has reduced the local increasing trends in frequency/duration of CoHot by 20% to 40%, and such mitigation effects are primarily induced by increased vegetation cover. Our results suggest that, reducing building volume density and promoting vegetation greening can mitigate the increasing risk of CoHot under global warming.