Excellent energy storage performance of dielectric capacitor is critical in modern electronic devices and power systems. However, the key component of dielectric composite may fail to function properly under severe service conditions, such as elevated temperature and great applied electric field. Here, the linear dielectrics of PI and PESU with high glass transition temperature (Tg) were proposed to improve the energy storage performance of composite, which hold the weakened carrier migration. The large band-gap of PESU and tight molecular chain of PI are beneficial for reducing leakage current density of composite, enhancing inter-molecular stability over a wide temperature and electric field range. Finally, the energy storage performance is improved by constructing a multi-layer structure with alternating outer layers. For instance, the discharge energy density (Ue) of 0.4PI-0.6PESU composite reaches 6.38 J/cm3 at 700 kV/mm and 80 °C. Significantly, the Ue of multi-layer 2/1/PVDF/1/2 composite is increased by 92.36 % at 80 °C and 400 kV/mm (from 2.88 J/cm3 to 5.54 J/cm3), and the efficiency (η) of it keeps at 68.5 %. Meanwhile, it owns a good cycle stability after 50,000 cycles with η > 90 %. This work provides a new direction of developing dielectric composite serving in severe service conditions for capacitors.