The invention discloses an optimal configuration method for a power grid side and user side energy storage system capacity, and aims to provide a way for optimally configuring the power grid side anduser side energy storage capacity according to the economy of the power grid side energy storage and user side energy storage when the energy storage system of a certain region is planned. On a premise that power supply reliability is met, the economic benefit of the energy storage system in the whole region is optimized, and the investment of the engineering construction of the energy storage system is saved. The optimal configuration method for the power grid side and user side energy storage system capacity comprises the following steps that: (1) according to the economic benefit sources ofthe energy storage system under different application scenes, independently establishing power grid side and user side electrochemistry energy storage economic model; and (2) utilizing a cooperativegame method to carry out optimal calculation on the economic model to finally obtain the optimal strategy combination of power grid side and user side energy storage system capacity configuration.