Abstract: With rapid developments of new energy systems, electric vehicles and other environmental protection industries, capacitor energy storage mediums are required to have stable and high energy storage density, as well as high energy storage efficiency in a wide temperature range. The commonly used BOPP film is difficult to meet the growing demands for energy storage equipment due to its low energy storage density and narrow working temperature, thus the development of new polymeric medium energy storage film becomes a research hotspot. Based on the previous research on the epoxy electrically polarized energy storage films with excellent energy storage performance at abnormal temperature, the comprehensive energy storage performance is further improved by adjusting the segment saturation, which is controlled by the ratio of benzene ring and hydrogenated bene ring in the molecular structure of epoxy. The research shows that, when epoxy resin is used as the matrix, and aromatic amine curing agent is completely or part replaced by aliphatic ring curing agent, not only a high working temperature can be ensured, but also stable and extremely-high energy storage efficiency can be reached, reaching 2.1 J/cm³ at 100 ℃ while maintaining a high energy efficiency of 99%. At last, the loss mechanism of the epoxy films with different segment saturation are analyzed by leakage current and high-voltage dielectric spectroscopy. It is found that the loss modes of the benzene ring and hydrogenated bene ring are different, which further confirm the feasibility of improving the comprehensive energy storage performance of the epoxy film by regulating the saturation of molecular chain segments.