The invention relates to a charge-discharge control method and system of an energy storage system. The method comprises following steps: collecting the scheduling data and theoretical output value ofa photovoltaic power station, determining a light discarding period, a tracing plan period, a light discarding control strategy, and a tracing plan control strategy; during the light discarding period, executing the light discarding control strategy; and during the tracing plan period, executing the tracing plan control strategy. The discharge and charge of an energy storage system is realized. The method can improve the on-grid energy of a photovoltaic power station and reduce the measurement cost generated by insufficient tracing precision and thus greatly increases the profits of the photovoltaic power station.