The PCR-GLOBWB model was employed to simulate monthly runoff processes in the Yangtze River Basin under natural conditions and human-influenced scenarios. The Mann-Kendall mutation test was applied to delineate the baseline period and the impacted period. Based on standardized runoff index and generalized extreme value distribution, the range of extreme high flow and extreme low flow changes under two scenarios with different recurrence periods was calculated, and quantitatively evaluated the contribution of climate change and human activities to the evolution of extreme runoff in the Yangtze River Basin. The results indicate that climate change is the main contributing factor to the extreme high and low flow changes in the Yangtze River Basin. Climate change has intensified the severity of extreme high flow and l extreme low flow in the central part of the upper reaches and middle and lower reaches of the Yangtze River. The regional differences in the impact of human activities on extreme high flow and l extreme low flow are significant, alleviating the severity of extreme high currents in the Danjiangkou Reservoir and Sichuan Basin, but exacerbating the severity of extreme low flow in the middle and lower reaches.