Abstract: The paper investigates the ecological sound operation of the cascade reservoirs in the Lower reach of Yalongjiang River.Based on the type and arrangement of the cascade hydropower stations,two flow control cross-sections are proposed:one is at the downstream location of the division sluice for the Jinping-Ⅱ station,the another is at the backward position of the Ertan dam.25 flow variation control schemes are presented with respective to the ecological requirement of these two flow control points.Then,a longterm optimal operation model,which is to maximize the total output of power generation of the cascade reservoirs,is established and solved by using the dynamic programming method.The total power generation amount and reservoir release discharge process corresponding to each flow variation control scheme are obtained.These influences on total power generation amount of different ecological flow values at the downstream division sluice and flow variation limits on the release discharge of the Ertan reservoir are analyzed,the indicators of power losses to ecological flow needs are defined and their values are calculated.Lastly the fitness of the Ertan reservoir release discharge processes to the natural flow regime is evaluated.The result shows that the total power generation amount of the cascade reservoirs will decrease while the release discharge process of the Ertan reservoir approaches the natural flow regime.