Abstract: By using fuzzy cluster analysis with 6 parameters including water color, transparency, 5-day BOD, total-nitrogen, totaphosphorus and suspension substance, the dendrogram of pollution of Lake Donghu ecosystem, and therefore the pollution dynamics in the lake are given in this paper. In critical value of 0.88, the pollution dynamics can be divided into 11 grgups -3 Of heavy pollution, 5 of medial pollution, 2 of light pollution and 1 of relative cleanness. This result is in accord with those of other recent studies on Lake Donghu ecosystem. Discussions in relation to ecological application of recent fuzzy cluster analysis are also given in brief.