Nanoparticles were treated by short-chain polyamide acid molecules of different theoretical average polymerization degrees

and the treated nano dispersion liquid was incorporated polyamide acid solution of high pol- ymerization degree

then nano-composite films of polyimide were prepared by tape-casting. The dielectric properties of dielectric spectra

conduction current and corona-resistant were made

to figure out the influence of the short- chain polyamide acid molecules of different polymerization degrees on the dielectric properties of nano-composite films. The results show that： with the increasing of theoretical average polymerization degree

the dielectric con- stant gradually increase

and the dielectric loss decrease

the electrical degradation threshold increase. The films show longer corona resistance time than the film without being treated

and with the increasing of theoretical average polymerization degree

the corona resistant time gradually decline.