The invention relates to a control method and device for automatic gain control of an energy storage system. The method firstly issues a charge/discharge instruction and a charge discharge compensation amount according to the system basic loss and the obtained schedule, and calculates the actual charge/discharge instruction for AGC control on the energy storage system; then during the control process, when the system adjustment error is determined to be greater than a set error threshold, a charge/discharge correction cycle is entered; according to the number of adjustments in the charge/discharge correction cycle and the system adjustment errors obtained after each adjustment, a charge/discharge compensation coefficient is corrected, and the actual charge/discharge instruction is recalculated according to the corrected charge/discharge compensation coefficient. The charge/discharge compensation coefficient is corrected according to the system adjustment errors obtained after each adjustment in the charge/discharge correction cycle, and thus, the change of the system basic loss caused by each reason is considered, and the energy storage system AGC adjustment precision is improved.