Disclosed is an method and apparatus for electric power distribution in an energy storage system. The electric power distribution method of the energy storage system (ESS) includes computing a total power amount on the basis of a received user output target power amount and a deviation amount, determining a power distribution power conditioning system (PCS) to which the total power amount is distributed out of the PCSs included in the ESS, and distributing the total power amount on the basis of the power distribution PCS. The deviation amount is a difference between an existing user output target power amount used in an existing power distribution process and an existing total power amount.