Abstract: Objective Taking the seal welds of pipe penetrations on the bottom head of the pressurizer in nuclear power plants as the object, an automatic in-bore tempering welding repair process is developed for such failed welds to exempt from post-weld heat treatment. Methods A 1:1 local feature structure based on in-hole surfacing repair of pipe penetrations is modeled using ABAQUS to simulate the tempering welding process. The designed tempering parameters are experimentally validated. Results The results indicate that the tempering parameters, with an effective temperature range of 250 ℃ to 650 ℃, pulsed current is 180 A/140 A, welding speed is 150 mm/min, wire feed rate is 450 mm/min, overlap rate is about 60%, inter-pass temperature T≤66 ℃, enable microstructure regulation except for the heat-affected zone near the weld toe after three surfacing passes, at the same time, without inducing new martensite degradation zones on the base material side. Weld toe zone exists a tempering blind zone due to special characteristics of the end structure of lap welds, which can be addressed by adding supplementary weld passes in the weld toe zone. Conclusion The established full-structure multi-pass tempering welding process simulation method demonstrates feasibility, providing rapid guidance for developing application-specific tempering repair processes. Further adjustments to the tempering temperature range can achieve precise microstructure control. The accuracy of tempering welding simulations is closely related to the accuracy of the weld model, particularly in the weld toe zone.