The study of ecological flow is a hot field in ecology and hydrology.However,the existing methodologies do not consider the functional integrity of an eco-system.In this study,we simulated the nutritional relationships between the communities of an eco-system in Xiaoqinghe river basin using the model of Ecopath.After determining the key fishes,we analyzed the velocity and water level demand of the key fishes by the habitat suitable index.Finally,coupling the velocity and water level demand of multiple speci...