[Objective] This study aims to investigate the non-stationary hydrological series and rainfall-runoff relationship in the main stream of the Huangshui River under the combined impacts of human activities and climate change, and to quantitatively assess the contributions of climate change and human activities to runoff variations. The findings are expected to provide a scientific basis for ecological protection, high-quality development, and optimal water resource allocation in the basin. [Methods] Based on hydro-meteorological data from 1970 to 2022 in the main stream of the Huangshui River, trend analysis, change-point detection, and periodic characteristics of hydrological elements were systematically examined using the Mann-Kendall trend test, Pettitt test, and wavelet analysis. Furthermore, the Simple HYDROLOG (SIMHYD) model was employed to simulate daily runoff processes, and a quantitative attribution framework was established to evaluate the contributions of climate change and human activities to runoff changes during different periods. [Results] The annual runoff series of the Huangshui River exhibited pronounced phased fluctuations, with no statistically significant overall trend (p > 0.05). At the Xining Station, the annual runoff decreased by 11.95%, 12.41%, and 12.09% in the three periods (1991–2000, 2001–2010, and 2011–2022) compared to the baseline period (1970–1990), with the contribution rates of human activities being 32.0%, 198.4%, and 328.6%, respectively. At the Minhe Station, the annual runoff changed by -16.99%, -9.48%, and +18.77% during the same periods, with the contribution rates of human activities being 67.13%, -136.37%, and 177.96%, respectively. [Conclusion] Quantitative evaluation revealed that the average contribution rate of human activities to runoff change of the Huangshui River exceeded 65%, and notably surpassed 100% after 2000, indicating that human activities have become the primary driving factor of runoff change. Climate change exhibited a positive effect on runoff recovery in certain periods, but its overall impact was secondary to that of human activities.