Abstract: On the basis of investigation from 1992 to 1993 on water quality, sediment, biology and pollution sources of the Qiandao Lake, the status of water environmental quality in the lake and total input of pollutants into the lake were comprehensively assessed. The results indicate that the water quality of the lake remains well, while pollution in some local waterbody increases with years and the trophic status tends to become mesotrophic level; non-point-source pollution load, 50% of which are inputted from the upstream rivers of Anhui Province, covers 95% of the total input load into the lake. A convection diffusion model of water quality were established and the water quality was predicted, and the countermeasures of water quality protectiion in the Qiandao Lake was suggested.