Abstract: The key technologies and research progress of lithium battery and supercapacitor hybrid energy storage system used for frequency regulation in auxiliary thermal power units were discussed, such as power/capacity optimization configuration of different types of energy storage, application of high-voltage cascade and modular multilevel（MMC） topology structure, and hybrid energy storage control strategies. The demonstration project of domestic hybrid energy storage assisted frequency regulation for thermal power units was introduced. Finally, the domestic development prospects of hybrid energy storage systems were prospected.