Developing renewable energy vigorously is an inevitable alternative to build a novel type of power system and promote energy transition. An optimal capacity configuration method of shared energy storage for micro-grid cluster with the multi-party bargaining game is proposed in this paper. Considering the collaborative interaction mechanism between micro-grid cluster operator (MGCO) and shared energy storage operator (SESO), a capacity optimization framework of micro-grid cluster with shared energy storage is established. Considering the energy sharing among microgrids and the capacity leasing mechanism of shared energy storage, a capacity optimization model of micro-grid cluster considering energy sharing is constructed. Then, the optimal capacity configuration model of SESO is built with dynamic leasing of shared energy storage. On this basis, an energy storage capacity configuration model for MGCO and SESO based on the bargaining game is established, and a distributed solution method based on ADMM is proposed. Finally, the case analysis is carried out based on MATLAB, and the results show that the proposed energy storage configuration method can reduce the cost of MGCO while improving the benefit of SESO, which achieves a win-win effect.