Abstract: Conducting analyses of runoff evolution and its driving forces under changing environment is crucial for effective water resources planning and management.This study focuses on the upstream catchment of the Danjiangkou Reservoir, utilizing a comprehensive dataset of inflow runoff, precipitation, and potential evapotranspiration from 1933 to 2023.Based on Budyko equation, the driving forces of climatic factors and human activities on runoff variations were quantitatively analyzed by the elasticity coefficient method and the decomposition method, and the results of two methods were comparatively evaluated by the ABCD hydrological model.The findings revealed that: ① from 1933 to 2023, average annual rainfall increased while annual inflow runoff decreased, though neither trend was statistically significant.In contrast, annual potential evapotranspiration exhibited a significant increasing trend after 2000.② The time series of annual inflow runoff, precipitation, and potential evapotranspiration revealed significant periodic changes with cycles of 9.3, 9.3 a, and 2.3 a, respectively.③ A notable change in annual inflow runoff occurred in 1985, after which the sensitivity of runoff to rainfall, potential evapotranspiration, and underlying surface characteristic parameters increased.④ The attribution analysis results obtained from the decomposition method closely aligned with those from the hydrological model.Based on the results by the decomposition method and hydrological model, the contributions of climate factors and human activities to the reduction of runoff in the Danjiangkou Reservoir basin were found to be 66.84% and 33.16%, respectively.This study highlights the dual impacts of climate change and human activities on runoff reduction and provides valuable insights for the rational allocation of water resources in the upper Hanjiang River Basin, as well as for the sustainable operation of middle route of South-to-North Water Diversion Project.