Abstract: Water resources system has various functions that influence or restrict each other. To coordinate the conflicts between different beneficial goals of a reservoir, we developed a method how to add a line of priority control to reservoir operation curve and applied it in a case study of Hunanzhen cascade reservoirs. In the application, the control line was used to direct the reservoir manager's decision to put the priority on water supply or power generation to reconcile the conflicts between the water demands by Hunanzhen and the reservoirs. A mathematical model for optimization of reservoir operation under priority line control was developed and solved with an immune evolutionary particle swarm optimization. The results show that it can improve the comprehensive benefits via reasonable priority decision in reconciling various water demand conflicts.