This paper summarizes the principle, basic requirements, and characteristics of thermal energy storage technology, and illustrates the key technologies of thermal energy storage, including the physical property optimization technology of thermal energy storage material, heat transfer enhancement technology of thermal energy storage, thermal energy storage material preparation technology and system control and optimization technology of thermal energy storage. Besides, the demands of thermal energy storage technology on the power supply side, grid side, and user side are analyzed, and its technical feasibility and economy are evaluated. Finally, according to the different application environments of thermal energy storage technology, the engineering applications of medium and high-temperature thermal energy storage technology and low-temperature thermal energy storage technology are expounded, including the solar thermal power station, power peak shaving, industrial waste heat recovery, solar cross-season utilization, cold chain transportation, air conditioning energy saving, refrigerator refrigeration and human body/building intelligent temperature regulation. This paper makes a comprehensive summary and analysis of the current development status and prospects of thermal energy storage technology, which can provide a certain reference for the follow-up research work in this field.