Abstract: In order to investigate the effect of nano doping properties of non-solvent impregnating varnish on polyester imide，this paper adopts micro-emulsion method and supercritical reaction preparation of nano SiO2 and according to different proportions of polyester imide solventless impregnating varnish was doped，curing at high temperature by different doping ratios of nano composite materials. After TEM characterization，dielectric strength， volume resistivity test，dielectric constant test and viscosity test，the sample results show the nanometer SiO2 and good compatibility in the matrix; when the doping amount is 10% breakdown strength than pure paint increased 5. 79% reoching 23. 04kV/mm; volume resistivity unchanged; dielectric constant with the doping amount decreased，and the increase of doping amount of viscosity has decreased substantially.