Abstract: In order to master the excitation laws of partial discharges(PDs) on the epoxy insulation surface under complex working conditions such as AC superimposed impulse, the characteristics of PDs of metal particle on epoxy insulation surface under AC superimposed lightning impulse(LI) voltage are experimentally investigated in SF₆ gas. When the AC voltage is lower than the partial discharge inception voltage(PDIV), the PDs excitation characteristics of metal particles with specific size and position under AC superimposed LI voltage are investigated.Meanwhile, when the AC voltage is greater than the PDIV, the effect of lightning impulse on AC partial discharge is studied. The results show that the PDIV decreases as the length of the metal particles increases, decreases as the diameter of the metal particles decreases, and decreases as the distance between the metal particles and the high-voltage electrode increases. The AC PDs excited by LI is more severe than the AC voltage applied alone. When the AC voltage is lower than the PDIV, the AC PDs excited by the negative LI(NLI) is more severe than that excited by the positive LI (PLI). When the AC voltage is higher than the PDIV, the LI has a negligible effect on the AC PDs.