Abstract: A series of nano SiO₂-Al₂O₃/polyimide(SiO₂-Al₂O₃/PI) of five layer structure corona resistant film A_m A_n PA_n A_m were prepared by dipping method, the middle layer (P) was pure PI film, the outer layer (A_m) and the secondary layer (A_n) were nano SiO₂-Al₂O₃/PI composite film doped with different SiO₂-Al₂O₃ mass fraction. The microstructure, dielectric properties and mechanical properties of five layer nano SiO₂-Al₂O₃/PI composite film were characterized by TEM, FTIR, broadband dielectric spectrometer, conduction current tester, corona resistance tester, dielectric strength tester and tensile test machine. The results show that the organic/inorganic composite structure is formed in the doped layer of five layer nano SiO₂-Al₂O₃/PI composite film. The protection of SiO₂-Al₂O₃ nanoparticles is the main factor affecting the corona resistance of five layer nano SiO₂-Al₂O₃/PI composite film, and the corona resistant life of five layer nano SiO₂-Al₂O₃/PI composite film A₃₂A₁₆PA₁₆A₃₂ is the most, which is 23.4 h. The amount of doping in the outer layer has a great influence on the dielectric strength of the five layer composite, the dielectric strength of the composite film A₂₀A₂₈PA₂₈A₂₀ is the largest, which is 302.3 kV/mm. By designing composite structure of five layer film, the mechanical properties of the five layer nano SiO₂-Al₂O₃/PI composite film can be improved as well as the corona resistant life and dielectric strength of the material.