Abstract: Nano-doping has a great influence on electrical properties of polymeric dielectrics. Taking pure polyimide 100 HN and nano-doping polyimide 100 CR from Du Pont as research materials, experiments on high-field conductance, surface potential decay（SPD）, DC breakdown and corona-resistance were carried out. The experimental results show that the DC breakdown strength of 100 CR decreases by 6.4% compared with 100 HN, whilst its corona-resistance time increases by 400%, indicating that the nanoparticles could play different mechanisms in two performances. The trap parameters extracted from SPD results indicate that the deep trap energy and density for 100 CR are both reduced. The high-field conductance results indicate that conductivity and carrier mobility are both increased for 100 CR. The eroded surface morphology after corona by scanning electron microscope show groove channel of 100 HN and layered rings with different erosion degrees of 100 CR, and the eroded area of 100 CR is enlarged. It is concluded that the nanofillers affect the conductance characteristics by changing the trap characteristics, and finally affect the DC breakdown performance. For the corona-resistant mechanism, a synergistic effect of surface collision scattering and charge dissipation is proposed to interpret the layered rings and better corona-resistance performance of nanocomposite.