Abstract: A large scale of waterpower projects have been and will have been constructed in the main upper and middle reaches of Yangtze River and its tributaries. According to the completed plan and construction step cascading reservoirs along these rivers will appear in future 20~30 years. Based on hydrological observation and data collected over last 20 years the change of water flow and sediment in Yangtze River and their occurrence reason were analyzed. With some observations to a few completed reservoirs,the impact manner and degree of sediment transportation rule were discussed. Finally some measures and proposals to decrease environmental effect as cascading reservoirs were suggested. It appeared that the flow and sediment process have changed, and sedimenttransporting quantity have obviously reduced in most river channels. Cascading reservoirs are one of the most important factors inducing the decreaes of sedimenttransportation . Cascading reservoirs not only decrease sediment transportation and runoff, but also significantly change natural water flow and sediment process. All of these may influence the environment of middle , down streams and estuary of the river. In order to reduce the effect on river features after the completion of cascading reservoirs, it is necessary to change the way in which the river is exploited for hydropower and is manipulated for flood control. Using flood to scour sediment and optimizing cascading reservoirs regulation will maintain nature river at a possibly natural condition.

Key words: Yangtze River, cascading reservoirs, sediment, ecological environment impact, storage volume