Due to the practical shortcomings of the classical deterministic pollution assessment model, the theory of trapezoidal fuzzy numbers was introduced to the environmental assessment system. A fuzzy risk assessment model was built based on the geoaccumulation index and biotoxicity coefficients of heavy metals. Using the fuzzy pollution risk assessment model, the risk of heavy metal pollution was evaluated for the surface sediment of Dongting Lake. The results showed that the pollution risk in a descending order was Hg > Cd > Pb > Cu > Cr > Zn > As, with Hg,Cd and Pb being the priority pollutants in Dongting Lake. Both the intervals of possible values for the geoaccumulation indexes of heavy metals and their credible levels were calculated using this model. Compared with the results of the deterministic assessment model, the fuzzy pollution risk assessment model gave a better characetriztaion of the actual pollution status and spatial distribution difference of the heavy metals in the sediment of the studied region which is more objective and comprehensive.