Based on analysis of the effect of the cascade development of hydropower in the upper reaches of Minjiang River on the ecological environment,this paper developed the method to calculate the minimum environmental water demand for maintaining ecological balance.The calculation showed that the water demand of ecological environment of Minjiang River basin accounted for 6%~33% of the annual average flow,the closer to the source of Minjiang River,the greater proportion of the water demand.This paper suggested increasing the eco-environmental water...