Abstract: For the participation of thermal power units in secondary FM with the assistance of energy storage system, a coordinated control strategy for the participation of energy storage system in secondary FM is proposed by fully combining the advantages of the two control modes of regional control deviation and regional control demand. The control strategy is based on the intersection of the time-domain response curves of the ACE and ARR signals to determine the switching timing of the two control modes, and then determines the energy storage output strategy for different FM regions according to the FM signal partition and the energy storage charge state, so as to enable the energy storage to achieve coordinated and optimized operation in the FM process. Simulation results show that the control strategy proposed in this paper can improve the FM capability while having a good effect of maintaining the energy storage charge state.