Abstract: Based on the observational precipitation and streamflow data in the Yanhe River basin during 1952-2008, the Mann-Kendall test was applied to investigate the trends of precipitation and streamflow. The effects of precipitation change and human activities on streamflow were quantified during the period of 1995-2008. The results indicate that the normal precipitation year accounted for 80.7 %, and most years were charactered by lower and low flow. Annual precipitation and streamflow both exhibited decreasing trends, and their abrupt changes occurred in 1995 and 2005, respectively. Compared with the baseline period of 1952-1994, the reduction of precipitation and streamflow in the period 1995-2008 was 11.1% and 27.3%, respectively; precipitation change contributed 46.2% to streamflow reduction, while human activities resulted in 53.8% of streamflow reduction.