Abstract: Epoxy resin insulating casing is widely used in high-voltage electrical equipment because of its excellent insulating properties and mechanical properties. However, long-term operation in a humid and dirty environment will lead to electrical ablation defects on the surface of the casing, which in turn will lead to discharges, flashovers and other faults, seriously threatening the safe operation of power equipment. In order to study the impact of electric ablation on the electric field distribution and insulation state of epoxy resin insulating casing, this paper analyzes the influence of ablation depth and position on the electric field distribution characteristics of casing based on electrostatic field theory and finite element simulation. Simulation results show that: Electric ablation will significantly increase the casing surface electric field intensity, especially in the flange position, the electric field concentration phenomenon is particularly obvious. And with the increase of ablation depth, the electric field distortion is further aggravated. In addition, the effect of ablation position on the electric field distribution is more significant. The results of the study clarify the location of the weak point of the epoxy resin insulating casing insulation, and reveal the mechanism of the impact of electrical ablation on the insulation state.