River runoff is related to water security in the downstream region, and it is vital to water resources management to conduct reliable assessment to the impacts of climate changes and human activities. This paper presents an analysis on the impacts of these two factors on mean annual changes in the runoff of the Bahe River in Shaanxi, using the Kendall rank correlation method for temporal trends and based on the records of precipitation, evaporation and runoff at the Luolicun and Maduwang hydrological stations in the period of 1959-2010. The Mann-Kendall test and accumulative anomaly method were used in this study to detect the statistically significant change points in hydrometeorological series, and ratios of slope changes in cumulative quantities were compared to quantify the relative effects of climate and human factors on runoff variation. Results show that in this period, no change point was detected in the runoff of upper Bahe, while in the midstream runoff of 1988 a significant steep drop in the streamflow occurred, thus showing an evident change point. This rapid change indicates that, on the upper stream runoff, human activities had a relatively small effect but climate change was the main factor; on the midstream runoff after 1988, both climate and human factors played major roles in causing the significant runoff drop. Decomposition results reveal that, to the variations in the upper stream annual runoff, the two factors contributed 97% and 3% respectively, while in the midstream case the corresponding contributions were 37% and 63%. Overall, human impact was dominant in the runoff decline of the Bahe River basin.