Abstract: Thermal energy storage in underground coal mining is a crucial approach to achieving the transformation and upgrading of mines. The cemented backfill material for enhanced thermal energy storage not only improves the utilization rate of coal-based solid waste resources, but also ensures the efficient consumption and utilization of renewable energy. The research status of backfill mining is analyzed based on the current coal mining technology and the scientific concept of "cemented backfill material for flexible enhanced thermal energy storage (CBM–FETES)" is proposed by integrating the idea of functional filling. The core of CBM–FETES is to ensure the four essential conditions: the suitability of geological conditions, the feasibility of thermal storage and extraction technologies, high efficiency in heat and mass transfer, and the safety and stability of the operational cycle. The key to achieving the efficient operation of CBM–FETES is to improve the thermal energy storage and extraction efficiency, enhance the sealing of the thermal storage system, and ensure the stability of the surrounding rock. The impact of factors such as heat source temperature, heat transfer distance and the circulation velocity on the heat extraction efficiency is analyzed, and thus the efficient heat extraction technique for CBM–FETES can be developed. Moreover, the efficient heat exchange design method for thermal energy is established based on the above analysis. During the process of thermal energy storage and extraction, micro-mechanisms of aging deformation and damage in backfilling body is revealed and the stability prediction and evaluation system is constructed based on the analysis of the thermodynamic characteristics of backfilling body. The technical path of CBM–FETES revolves around the following strategic mainline: pre-mining geological conditions → dynamic parameters response of backfilling body during mining → coupling effect of buried pipes, backfilling body and surrounding rock → coordinated development of mining underground space and variable energy. The planning and design of operational parameters for the thermal energy storage system is conducted by integrating the wind-solar hybrid concept, exploration and site selection for thermal storage layers, advanced planning of thermal storage filling systems and preparation of high-efficiency thermal storage materials. Based on mining theory, geological support theory and engineering technology system of CBM–FETES, which integrates coal mining, geological engineering, and ecological environment technologies, is established. In general, CBM–FETES realizes the full integration of mines and variable energy sources and enriches the connotation of filling mining. In addition, CBM–FETES proposed in this paper can provide theoretical references and practical examples for the development of renewable energy in coal mining areas and promote the transformation and utilization of mines in China.