Fuxian Lake is a deep lake with a capacity of 184×10⁸ m³. Based on the incessant monitoring statistics during 1980-2000, the water quality as well as the eutrophication status was revealed in Fuxian Lake,.i.e. the phytoplankton density increased 2.6 times, Chl.a 3 times while SD decreased~50%. Comprehensive assenssment of nutrient status and evolution during the past 20 years indicated that a sharp growth of TSI would bring out a potential possibility and danger of eutrophication which has compelled us to take some efficient, effective measures to protect the lake from further deterioration or invaluable lose both economically and ecologically in the future would be seen.