Climate change-induced shifts in plant phenology have substantially impacted terrestrial ecosystem structure and function. While the effects of drought and heatwaves on leaf senescence have been studied, the response of leaf senescence to compound drought and heatwave events remains poorly understood, especially due to a lack of experimental evidence. In this study, we investigated the responses of leaf senescence to varying durations of compound drought and heatwave stress (13, 28, and 43 days) in saplings of three tree species with differing drought tolerance. We found that prolonged drought and heatwave conditions delayed leaf senescence by 20.2 and 22.4 days in Koelreuteria paniculata and Hibiscus syriacus, respectively, potentially due to carbon sink limitation. However, Acer palmatum exhibited a nonlinear response, with leaf senescence shifting from delayed to advanced as the compound stress was prolonged, likely due to its low drought tolerance. Additionally, total photosynthesis, relative height increment, and basal diameter growth decreased in all three species, with the most pronounced reductions observed in Acer palmatum, followed by Hibiscus syriacus and Koelreuteria paniculata. Our findings demonstrate nonlinear and interspecific differences in leaf senescence responses to compound drought-heatwave events, contributing to a deeper understanding of plant phenology under climate change.