The present invention provides a modeling method and system for evaluating aggregation frequency modulation performance of a distributed energy storage system. A method and system can be implement bydetermining a power grid aggregation target, and calculating the response factor of each distributed energy storage unit of the distributed energy storage system to the power grid aggregation frequency modulation, combining with the preset constraints of distributed energy storage system and power grid, adopting particle swarm optimization (PSO) to optimize the pre-established objective function of power system, determining the optimal aggregation frequency modulation scheme of distributed energy storage system, and then performing simulation analysis on the economy of the grid before and after the access of distributed energy storage system according to the preset model on the simulation model,so as to evaluate the frequency modulation performance of distributed energy storage system after the access of distributed energy storage system to grid. By optimizing the output of the distributed energy storage system, the method and the system realize the timely treatment of the frequency problems existing in the power grid, prevent the occurrence of large-scale cascading failures, and give full play to the application potential of the distributed energy storage system.