Abstract: The energy storage system can effectively reduce the volatility caused by more and more renewable energy sources in the power grid, improve the utilization rate of renewable energy and the stability of system. In this paper, the optimized operation mode and capacity configuration method of pumped storage station in a renewable energy grid are studied by taking the practical energy storage facility as an example. The pumped storage station is operated under its capacity constraints, and it is divided into the energy storage condition and the power generation condition by positive or negative of the unbalanced power in the grid. On this basis, this paper puts forward the way of the pumped storage station participating in the power grid generation plan: Pumped storage station does not participate in the actual day-ahead power generation plan only plays a reserve role, in the real-time generation plan, the pumped storage station is preferentially called to equilibrium the deviation between day-ahead forecast value and real-time forecast value of equivalent load. The mathematical model of this method and the optimization method are also given. In addition, the capacity of pumped storage station is planned and designed by the method of probability statistics. Finally, through the analysis of the simple system with four elements and single busbar, the feasibility of the optimized operation mode is verified, and the sensitivity of the capacity of the pumped storage station is discussed qualitatively based on the operating cost of the conventional power grid.