The upper and middle reaches of the Taoer River, a representative ecologically sensitive area, has experienced great cli-mate change and rapid agricultural and industrial development since 1961. There is therefore an urgent need to evaluate the impact of climate change and human activities on stream flows to serve better the water resource management in this region. The nonparamet- tic Mann-Kendall test and moving t-test were used to identify trends and change points in stream flow, precipitation and potential evapotranspiration data series. A significant upward trend has been found in annual stream flow, with an abrupt change identified in 1985 at the Taonan station which is the station that controls the entire study area. The stream flow data was divided into a baseline period and a period of change. Both Fu and Zhang's functions were employed to evaluate the impacts of variation in climate and human activities on mean annual stream flow, based on precipitation and potential evaporation. Analysis of the increase in mean annual stream flow between the baseline and the period of change indicated that climate change accounted for about 45% of the total increase and human activities were responsible for about 55%.