With the transformation of energy structure from traditional thermal power to new power system with renewable energy as the theme, the randomness and fluctuation of new energy bring challenges to the stability of power grid. Conventional thermal power units may not meet the K value requirement of comprehensive frequency modulation performance index due to large mechanical inertia and slow response speed of frequency modulation. Energy storage system assists traditional thermal power joint frequency modulation, which can speed up the adjustment response rate and effectively improve the frequency modulation performance of the system. In this paper, the control strategy and performance evaluation of supercapacitor-battery hybrid energy storage participating in power grid frequency modulation are studied. The secondary frequency modulation simulation model of fire storage coupled system based on MATLAB/SIMULINK is established, and the frequency modulation allocation strategy based on SOC adaptive is adopted. Compared with particle swarm optimization algorithm, genetic algorithm and harmony search algorithm, particle swarm optimization algorithm is selected for capacity optimization configuration. The results show that the control strategy and capacity allocation scheme can effectively improve the technical performance and economic performance of thermal power unit frequency regulation.