Using survey information about pollution sources and water quality monitoring data, water quality condition was analyzed systematically. The result displayed that water quality in the upper reach was obviously better than that in the middle-lower reaches. Water quality was Inferior Class V and showed worse trend, with serious excess of contents of DO, COD, CODMn, BOD5, NH3-N in the middle-lower reaches. Based on the water quality change trend, influence which affected water pollution possibly on land use, urban life and industry activities were discussed. As application rate and loss of fertilizers and content of NH3-N heightened with the increase of cultivated land area, rural activity was the major factor affecting water quality in village and town. Discharge of living pollution and industrial pollution led to water quality deterioration.