Based on the data of water quality parameters sampled monthly from six stations of Lake Dianshan in 2004,the author aimed at evaluating eutrophic status and quality grades with the grey-clustering method.Water quality parameters of DO,BOD_5,COD_(Mn),TP,NH_3-N,Chl.a in Lake Dianshan monthly means ranged at 7.210-(9.943)mg/L,3.810-4.940 mg/L,6.016-7.053 mg/L,0.137-0.366 mg/L,2.1763.362 mg/L,29.814-(56.02) mg/m~3 respectively.The evaluating results showed that(1) Lake Dianshan was in the eutrophic status at six sampled sations;(2) the water quality of this lake was in V-grade level.In the process of evaluation by grey-clustering method,TP,NH_3-N,Chl.a were found to be the most important water quality parameters which contributed to eutrophic status and quality grades.The article suggested the effective measures to improve the water quality of Lake Dianshan are to remove the surplus nitrogen and phosphorus by planting the aquatic grass,and to restrain the algae blooming by rearing the filter fish.