Abstract: The in-situ sol-gel method was employed to prepare nano-alumina/PI hybrid composite. The chemical structure，morphology，the corona-resistant lifespan and thermal property were characterized by the method of Fourier transform infrared spectroscopy (FTIR)，atomic force microscope (AFM)，scan electric microscope (SEM) and thermogravimetric analysis (TGA). The micrographs of AFM and SEM indicate that nano-alumina particles are finely dispersed in the polymer resin. The sizes of alumina particles are 40～100 nm. The solid content of nano-alumina influences the corona-resistant lifespan and thermal-resistance. The corona-resistant lifespan and thermal decomposition temperature are increased with increasing the solid content. When the mass fraction of nano-alumina is 16% Al₂O₃/PI， the width of sample is 25 μm and breakdown strength is 60 kV/mm, its corona-resistant lifespan is 130 h，rising 11 times，its thermal decomposition temperature is 498.63℃，rising 20℃，and the shear strength is a little lower than that of the pure material.