Large scale renewable energy such as wind power grid, photovoltaic grid and others has brought great challenges to the grid's afety and stability. Energy storage system should be configured so as to stabilize the power fluctuation and achieve energy smooth transfer. Under the application scenario of photovoltaic power plant，the echelon battery storage' optimal planning is analyzed in the mode of stabilizing the photovoltaic power fluctuation . Economic evaluation is assessed. The optimal planning and economic evaluation model of the photovoltaic power plant energy storage system is established to meet the minimum storage capacity cost under the limit of the grid fluctuation ratio. The artificial fish swarm algorithm is used for solution optimization, and the economy evaluation of echelon battery is assessed and compared with conventional energy storage system. The results show the rationality and validity of the model.