Cross-regional power transmission of large-scale hydro-wind-photovoltaic bases is an important form to support renewable energy development. This paper proposes a coordinated electrical energy storage (EES) configuration method for both source and load sides. Typical scenarios are solved using. . In this paper, a large-scale clean energy base system is modeled with EBSILON and a capacity calculation method is established by minimizing the investment cost and energy storage capacity of the power system and constraints such as power balance, SOC, and power fluctuations.