Hybrid energy storage system is to use flywheel energy storage system and long-term energy storage system in a certain proportion. When the grid frequency is frequently disturbed, the flywheel energy storage system bears most of the output. When the flywheel energy storage system cannot meet the requirements, the long-term energy storage can supplement the power or energy. Hybrid energy storage system can minimize the actions of electrical devices, improve the service life and safety of the overall system, and realize the economy of the energy storage system under the double rules.