Floristic composition, distribution and biomass of aquatic vegetation were investigated in 3 major parts (Tanglinhu, Guozhenhu and Houhu) of Lake Donghu, Wuhan during 1988 1993. Results were compared with the historic studies conducted in the past 30 years. All aquatic plant species of 3 families recorded in 1963 were found to disappear in this study. totally 14 species in 7 families were found to disappeared in the last 30 years as well. Four newly recorded species belong to 4 families. Distribution of the submersed vegetation was 1-28% of the lake areas, much less than that in 1963. Biomass dynamics indicate the degradation of the submersed vegetation still occurs in the recent years after the extinction of the dominant species and the remarkable succession of the vegetation during 1970s. Of 3 major lake areas alage appeared to dominate the submersed macrophytes in biomass in Guozhen and Houhu Lake area. Vegetation biomass had fluctuated strongly in Tanglin Lake area from 1970s. Vallisneria spp. and Myriophyllum spicatum start to dominate the submersed vegetation as the result of the vegetation succession continuing in the recent years. Biomass and frequencies of the major species decreased drastically and the biodiversity changed periodly along with the succession of the dominant species. Statistics indicated the environmental impacts on the growth of all species of submersed vegetation. The most possible factors which led to the degradation and succession of submersed vegetations were tested and discussed.