Abstract: Aiming at the problem of high repair rate of thermal defects of high voltage isolation switch in Xuejiawan area, this paper summarizes the repair parts of thermal defects, and analyzes the main causes for the repair are the increase of the contact resistance caused by coating oxidation and the ablation of contact surface. A mathematical simulation model of high voltage isolation switch temperature based on thermodynamic theory is established to analyze the correlation among the contact resistance, the ablation area and the temperature rise. Through the field test analysis for the influence factors of contact resistance and ablation area, that is the plating cleaning, corrosion spot welding and plating to repair the relationship between temperatures, and on the basis of the existing maintenance process improvement, with laser cleaning technology of the oxide layer, the cold welding technology welding point ablation, cyanide-free brush silver plating process to repair coating. After continuous tracking statistics of 3 years, the repair rate of the thermal defects decreased from 41.19% to 7.75%.