Abstract: The water injection system of Daqing Oilfield is a complicated pressure system that is made up of several water-injection stations linked up with each other.At present,the system has problems of lower operation efficiency and higher energy consumption loss.It is an important technical measure to solve this problem by carrying out optimal operation of water injection systems.With the minimum injection energy consumption as the objective function,the hydraulic equilibrium of the system,injection rate and injection pressure as the constrained conditions,both displacement optimization model and starting-stopping scheme optimization model of water injection pumps are constructed,which are solved with penalty function method and hybrid genetic algorithm individually.Relevant optimal operation software for the water injection system has been developed.The economic benefits of cutting down the specific energy consumption for water injection system by 0.32 kW·h/m3 and saving the electricity consumption by 2.32×104 kW·h/d are gained in real application.