Abstract: Reservoir group co-regulation in small watershed considering ecological flow has been an important approach to improve the ecological environment. A multi-objective co-regulation model of reservoir group in small watershed considering ecological flow is constructed by reservoir group operation simulation and optimization approach. In the model, the reservoirs are classified as 3 kinds according to the reservoir regulation capacity and regulation objectives and the dispatching mode and dispatching diagram of reservoir group are determined by taking the water supply as priority objective. On the above basis, the joint dispatching diagram of reservoir group is solved by multi-objective genetic algorithm (NSGA-II). Taking the Longxi River watershed as a study case, the benefit of multi-objective regulation of reservoir group under different ecological water demands are compared and analyzed. The results show that the increase of ecological water would impose the largest impact on agricultural water use.