By the analysis of water quality monitoring data of Dongting Lake watershed in 1989,1997 and 1999,it indicated that phosphorus pollution was particularly heavy,but the highest concentration of the heavy metals except Cu in each yearwas all lower than statewater quality standard grade Ⅱ;water pollution levels increase year after year at a high rate, except contam ination TN;point sources make a greater contribution to the pollution of Dongting Lake watershed and concentrations of the contam inates are higher in low water season than in high water season and tap water season. Due to the shortage of research on toxicity harmfulness coefficients of TN and TP, their values are obtained through an extrapolation approach using toxicity coefficients of heavymetals determ ined abroad. The coefficients are applied furthermore to risk analysis of pollution in Dongting L akewatershed. The research results show that TP contributesmost to the pollution risk in Dongting L ake watershed, while TN and Zn contribute relatively less.A dditionally, the risk coefficient value at Junshan monitoring site is relatively high, which poses potential ecological risk for its circum ference ecosystem.The risk values at other monitoring sites are lower and the potential ecological harm is minimal .