The variation of base flow is a comprehensive reflection of the change of regional climate and human activities, and it is an important element to maintain sustainable development of the ecosystem. In this study, the Kuye River catchment, a tributary of the Yellow River, with a drainage area of 8706 km² on the Loess Plateau, was chosen to investigate the change trends and evolution characteristics of base flow. Based on Chapman-Maxwell base flow separation technique, the total runoff from Wenjiachuan hydrological station, which is the maximum control station in the Kuye River catchment, was separated into surface runoff and base flow. The nonparametric Mann-Kendall test and the Pettitt test were used to identify the trends and change points in the base flow during 1959 to 2005. The results indicated that: (1) In the past 50 years, a significant negative trend was detected in the annual base flow in all 7 time periods. For total year period, the average change rate is 0.628mm/a. The change points significantly occurred in 1980 and 1996. (2) Analysis of flow duration curves showed that, compared to the contrast period from 1959 to 1979, the relative changes of annual base flow for 5%, 50% and 95% exceeding time were lowered by 30%, 38% and 54%, respectively, in the treat period from 1980 to 1995, and the relative changes of annual base flow for 5%, 50% and 95% exceeding time were lowered by 57%, 68% and 100%, respectively in the coal mining period from 1996 to 2005. (3) The significant negative trend in base flow is a comprehensive effect of the change of regional climate and human activities, and the main factor is that excessive exploitation of a large area of coal resources and utilization of groundwater.