The invention discloses an overhaul method of a 500KV transformer in a million kilowatt-grade advanced pressurized water reactor nuclear power station, comprising the following steps of: carrying out curvature measurement and insulation measurement on an iron core in the transformer to respectively obtain a curvature measurement result and an insulation measurement result; judging whether curvature correction and insulation correction are carried out on the iron core according to the curvature measurement result and the insulation measurement result; if so, executing curvature correction or insulation correction; and if not, finishing the overhaul of the transformer. By using the overhaul method of the transformer in the invention, the curvature correction and the insulation correction are carried out on the iron core in the transformer according to the curvature measurement result and the insulation measurement result of the iron core, the strength of the iron core is enhanced, and the one point earth of the iron core is ensured, therefore, the problems of curvature of the iron core and partial short circuit among frames of the iron core are solved effectively. The method provided by the invention is perfect in process and convenient to control and can be used for operation sites of the nuclear power station, therefore, the overhaul time and cost of the iron core can be effectively reduced.