After putting the first stage project of the Eastern Route of South-to-North Water Transfer from the Changjiang River into practice, the water lever of Hongze Lake, as one of impounded lakes, will rise averagely 0.5 m and tend towards stability.Therefore, the subsequence will bring about changes in ecological environment and aquatic organism In Hongze Lake.This paper discusses prediction of the above subsequence.According to the annual investigation (including physical and chemical charateristics of lake water, phytoplankton, zooplankton 9 zoobenthos) in permanent stations from Dec.1987 to Dec.1990 and comprehensive investigation in the whole lake in Sep.1989, the result shows: (1) Transparency will get decreased slightly in some water areas, but there is no change in the open water area, (2) If the water is diversed in a short period of time, the nutrient salts of the lake water will remain unchanged.However, if diversion of the water continues in a long period of time, inorganic nitrogen compounds may increase while dissolved phosphorus decrease; (3) Some areas will be a little abundant in plankton but not in whole lake; (4) Gastropods will decrease, but Corbicula flumtnea Muller Increase;(5) Aquatic vascular plants will decrease;(6) Open-water area fish will increase, but the yield of herbivorous fishes which lay eggs on aquatic vascular plants will somewhat decrease.