An energy storage system, wherein the energy storage system comprises at least one energy storage unit cluster, the energy storage unit cluster comprises at least two energy storage modules, and the at least two energy storage modules are connected in series; and the energy storage system further comprises a first bus, a second bus, and a centralized monitoring system of the energy storage unit cluster, wherein the second bus is a direct current bus; the energy storage unit cluster is coupled to the first bus by using a first converter; each of the at least two energy storage modules comprises one energy storage element group and one direct current DC/DC converter, wherein the energy storage element group is coupled to the second bus by using the DC/DC converter; and the centralized monitoring system is connected to the energy storage unit cluster through a control bus, and is configured to control the DC/DC converter in any energy storage module in the energy storage unit cluster to output a compensation current to an energy storage element group end or draw a current from an energy storage element group end, so that energy storage element parameters of all energy storage modules in the energy storage unit cluster are consistent; wherein the energy storage element parameter comprises one of a charging/discharging time, a state of charge SOC, a depth of discharge DOD, a state of health SOH, and a port voltage; wherein each of the at least two energy storage modules further comprises one battery management unit BMU; and the centralized monitoring system is connected to the BMU of each energy storage module in the energy storage unit cluster through a control bus, and a controller in a BMU of the any energy storage module is configured to control the DC/DC converter to generate the compensation current to the energy storage element group end or draw the current from the energy storage element group end, so that the energy storage element parameters of all the energy storage modules in the energy storage unit cluster are consistent; characterized in that a first input/output end of a DC/DC converter in any one of the at least two energy storage modules is coupled to an energy storage element group; and second input/output ends of DC/DC converters in all of the at least two energy storage modules are connected in series to each other, and then are coupled to the second bus. the energy storage unit cluster is coupled to the first bus by using a first converter; each of the at least two energy storage modules comprises one energy storage element group and one direct current DC/DC converter, wherein the energy storage element group is coupled to the second bus by using the DC/DC converter; and the centralized monitoring system is connected to the energy storage unit cluster through a control bus, and is configured to control the DC/DC converter in any energy storage module in the energy storage unit cluster to output a compensation current to an energy storage element group end or draw a current from an energy storage element group end, so that energy storage element parameters of all energy storage modules in the energy storage unit cluster are consistent; wherein the energy storage element parameter comprises one of a charging/discharging time, a state of charge SOC, a depth of discharge DOD, a state of health SOH, and a port voltage; wherein each of the at least two energy storage modules further comprises one battery management unit BMU; and the centralized monitoring system is connected to the BMU of each energy storage module in the energy storage unit cluster through a control bus, and a controller in a BMU of the any energy storage module is configured to control the DC/DC converter to generate the compensation current to the energy storage element group end or draw the current from the energy storage element group end, so that the energy storage element parameters of all the energy storage modules in the energy storage unit cluster are consistent; characterized in that a first input/output end of a DC/DC converter in any one of the at least two energy storage modules is coupled to an energy storage element group; and second input/output ends of DC/DC converters in all of the at least two energy storage modules are connected in series to each other, and then are coupled to the second bus.