Optimizing the high-temperature energy storage characteristics of energy storage dielectrics is of great significance for the development of pulsed power devices and power control systems. Selecting a polymer with a higher glass transition temperature (T_g) as the matrix is one of the effective ways to increase the upper limit of the polymer operating temperature. However, current high-T_g polymers have limitations, and it is difficult to meet the demand for high-temperature energy storage dielectrics with only one polymer. For example, polyetherimide has high-energy storage efficiency, but low breakdown strength at high temperatures. Polyimide has high corona resistance, but low high-temperature energy storage efficiency. In this work, combining the advantages of two polymer, a novel high-T_g polymer fiber-reinforced microstructure is designed. Polyimide is designed as extremely fine fibers distributed in the composite dielectric, which will facilitate the reduction of high-temperature conductivity loss for polyimide. At the same time, due to the high-temperature resistance and corona resistance of polyimide, the high-temperature breakdown strength of the composite dielectric is enhanced. After the polyimide content with the best high-temperature energy storage characteristics is determined, molecular semiconductors (ITIC) are blended into the polyimide fibers to further improve the high-temperature efficiency. Ultimately, excellent high-temperature energy storage properties are obtained. The 0.25 vol% ITIC-polyimide/polyetherimide composite exhibits high-energy density and high discharge efficiency at 150 ℃ (2.9 J cm⁻³, 90%) and 180 ℃ (2.16 J cm⁻³, 90%). This work provides a scalable design idea for high-performance all-organic high-temperature energy storage dielectrics.