The methods of comprehensive pollution index,double weight index,and Spearman′s rank correlation coefficient were used to evaluate the spatiotemporal variations in water quality of Weihe River in Shaanxi Province.According to the water quality data collected at 26 monitoring sections from 2005 to 2010,the temporal and spatial trends of COD and NH3-N and the driving forces were analyzed respectively.The results indicated that the overall water quality has improved certainly as shown by the reduction of COD.The water quality of Baoji section was classified as of the third grade.However,the pollution level in the section from Xianyang to Weinan City was still quite high.The polluted tributaries and drainage outlets in the areas of Xi′an and Xianyang City contributed mainly the pollution in the mainstream.