Guazhou County is located in the downstream of the Shulehe River Basin. The principal components were used to analysis thedata of human activities in Guazhou County and the annual average water quality data in Shuangta Reservoir from 1993 to 2008, and the information representing human agricultural and industrial activities and the reservoir water quality situations was obtained. Then, the multiple linear regression analysis was used to calculate four regression equations reflecting the impacts of human activities and land use changeson pH index, dissolved oxygen index, potassium permanganate index and chemical oxygen demand index of water environment in the reservoir. The results show that the main impacts on water quality in the Shuangta Reservoir are human agricultural activities and land usechanges, and the major pollution sources of water quality in reservoir are non-point source pollution aroused by human agricultural activities. In addition, the impact of human industrial activities on water quality is not obvious in the regression equation. And the reservoir isstill facing the risk of eutrophication. In the course of human agricultural activities, each increase of 10 thousands mu of cultivated land willcause the pH index increasing by 0.062, dissolved oxygen index dropping by 0.046, potassium permanganate index increasing by 0.103,chemical oxygen demand index increasing by 0.617; and each increase of 10 thousands tons of nitrogen fertilizer will cause pH index increasing by 1.837, and if the total population increase by 10 thousands, then the chemical oxygen demand index will increase by 0.798 as well.