A method for controlling an energy storage system includes: determining that a first battery cluster in a plurality of battery clusters needs to be calibrated; and controlling, based on a state of charge SOC of the first battery cluster and a current charging or discharging state of the energy storage system, the first battery cluster to be charged or discharged or to be in a standby state, so that the first battery cluster satisfies a SOC calibration condition. In the method, charging, discharging, or standby-state control needs to be performed on only one battery cluster that needs to be calibrated in the energy storage system, independent decoupling management is implemented on the battery cluster, and normal running of the energy storage system is not affected. This enables the battery cluster to quickly satisfy the SOC calibration condition and can improve SOC accuracy of the energy storage system.