In this paper, the subordinating degree of all assessment parameters of eutro-phication of lake to each eutrophication assessment grade is taken as a fuzzy set of the discourse field Ω of assessment parameters. The assessment grade of eutrophication state of lake is given by calculation and comparison of the fuzzy degree values of these fuzzy sets. This method has been applied to the eutrophi-cation assessment of 16 main lakes and the results comciue with that of the statistical method.