[Objective] The Hanjiang River Basin, as the core water source area of the Middle Route of the South-to-North Water Diversion Project, has runoff variations that are of great significance to water supply security and regional sustainable development. This study aims to identify the main driving factors of runoff evolution in the upper, middle, and lower reaches of the Hanjiang River Basin. By following the framework of “pattern identification-hydrological modeling-attribution analysis of runoff changes,” this study quantitatively and qualitatively assesses the impacts of climate change and human activities on runoff variations, thereby providing a scientific basis for rational water resources utilization and management decisions in the river basin. [Methods] Statistical methods, including linear regression, moving average, rescaled range (R/S) analysis, cumulative anomaly, Mann-Kendall trend test, and sliding t-test, were employed to identify the evolution patterns of hydrological elements. A distributed Xin’anjiang model was constructed to simulate and reconstruct natural runoff, and the contribution rates of climate change and human activities to runoff changes were quantified. [Results] The results showed that from 1959 to 2019, precipitation in the upper reaches exhibited a decreasing trend at a rate of -0.59 mm/a, whereas precipitation in the middle and lower reaches showed increasing trends at rates of 0.24 mm/a and 0.05 mm/a, respectively. Temperature differences among the three reaches were minimal. Runoff exhibited significant interannual variability, with an abrupt change occurring in 1990. The decline in runoff at the Xiantao station in the lower reaches was significantly larger than that at the Huangjiagang station in the middle reaches and the Shiquan station in the upper reaches. Climate change contributed to a reduction in runoff at Shiquan station by 75.97 mm, accounting for 59.98% of the total change. Human activities led to runoff reductions of 83.32 mm at Huangjiagang station and 78.45 mm at Xiantao station, with contribution rates of 54.89% and 77.20%, respectively. [Conclusion] The impact of human activities on runoff evolution is gradually intensifying and becomes more pronounced in the downstream areas. The upper reaches, characterized by higher elevation and dominated by forest and grassland with relatively limited human activities, experience a smaller degree of anthropogenic influence. In the middle reaches, higher population density and economic development drive greater water demand, while regulated water transfer from hydraulic engineering has led to an overall decline in runoff. In the lower reaches, intensive human modifications to the underlying surface, frequent human activities, high water demand, and large-scale regulated water transfers collectively result in a significant reduction in runoff. The findings of this study provide valuable insights for water resources development, utilization, and watershed planning in the Hanjiang River Basin.