The invention relates to a modular centralized energy storage system comprising a modular multilevel converter, an energy storage system interface, an isolated DC/DC circuit and an energy storage unit. An input end of the modular multilevel converter is connected to k-phase high-voltage alternating current, and an output end of the modular multilevel converter is connected to positive and negativehigh-voltage DC buses. The positive DC bus is connected to sub modules 1 to n through an upper bridge arm inductor to be connected to an i1 end of an energy storage system sub interface 20i, the negative DC bus is connected to sub modules n+1 to 2n through a lower bridge arm inductor to be connected to an i2 end of the energy storage system sub interface 20i, i=1, 2, to k, an output end of the energy storage system sub interface 20i is connected to an input end of the isolated DC/DC circuit, and an output end of the isolated DC/DC circuit is connected to the energy storage unit. According tothe topology of the invention, the disadvantages of the energy distribution imbalance of a traditional distributed energy storage unit and a feedback network side energy imbalance of a traditional centralized series energy storage unit are overcome, and a centralized energy storage system with high quality and a safe operation is provided for a power system.