As the largest tributary of the Yellow River , the Weihe River is the important earth''s surface water body in Guanzhong region of Shaanxi Province. With the rapid development of nation economy and the ascent of water consumption in recent years, the pollutant discharged into the Weihe River have increased year by year.The pollution of water quality in the Weihe River has been growing ,which makes the Weihe River lose its original function.The analysis of change characteristic of water quality has impoetant guide role for the pollution prevention of the Weihe River. On the basis of measured value from 19gauging station along the Weihe River in Shaanxi Province, the paper analyzed the variability of two main pollutants of COD and NH3-N. The result indicated that the values of both COD and NH3-N of 50% measured section are greater than the threshold values of surface water quality standard according to the water environmental functional district planning. Although the water quality of some section was still V grade, the concentration of COD and NH3-N appeared decrement tendency from 2007to 2011.