The invention relates to a control method of an energy management system for large-scale VRB optimized operation, which is characterized by comprising the steps of establishing a large-scale energy storage efficiency mathematical model; determining the total efficiency of the energy management system according to the large-scale energy storage efficiency mathematical model and a power-efficiency fitting relation of an energy storage unit module; and solving the number of energy storage units and the power of the energy storage unit module at each sampling moment, and the like. According to theinvention, the power-efficiency relation is fitted based on the charge-discharge simulation data of different stored energy powers, and the optimized operation mode of the number of energy storage participating charge-discharge modules is reasonably selected according to a specific energy storage charge-discharge power command by combining the structure of the large-scale VRB energy storage system. The analysis of examples shows that the control strategy can effectively improve the charge-discharge efficiency of the energy storage system, is conducive to the balance of the state of charge ofthe stored energy, avoids the situation that the same energy storage unit is over-charged or over-discharged and reduces the service life loss of the energy storage system. The control method has theadvantages of scientific and reasonable method, strong applicability, good effect and the like.