The status of water quality of the main river channels into Yangcheng Lake in recent years was analyzed. Several rivers with inferior water quality were found out, and the main pollutant indices were determined. Tendency analysis was conducted through calculation of the pollutant flux into the lake. The areas of major pollutant sources and the proportions of pollutant fluxes of the river channels were determined by comparing the pollutant fluxes of peripheral access to the quasi-protection areas and those of the quasi-protection areas directly into the lake. The results show that the water quality of major river channels into the lake levels off and there is no tendency of deterioration. Moreover, the pollutant flux of the western part of the lake mainly comes from the Litang River, and in the past five years the total pollutant flux of the quasi-protected areas directly into the lake has been greater than that of peripheral access to the quasi-protected areas, where the average annual growth rate of NH₃-N, which is the main pollution index, is the highest of all the pollutants.