Abstract: Al₂O₃ coating for electrical insulation was fabricated by spinning composite slurry containing boehmite sol,nano-sized α-Al₂O₃ particles and polyvinylpyrrolidone（PVP） additive.The results show that the addition of PVP changes the suspension stability of nanosized α-Al₂O₃ particles in composite slurry and finally adjusts the density and properties of obtained Al₂O₃ coating.When the molar ratio(x_PVP) of PVP to the Al³⁺ in boehmite sol is 1.2,the obtained coating is dense and uniform with the highest dielectric breakdown strength of ～67kV/mm.Because of the higher quantity of grain boundaries and interface defects of well-dispersed nanosized α-Al₂O₃ particles in coating,the space-charged polarization will be established and become the dominant polarization mechanism in coating,which largely influences the dielectric loss and dielectric constant.