Abstract: Taking the welding repair of 15CrMo steel as an example, the effects of welding speed, welding material specifications, surfacing pass and layer on the hardness and microstructure of the welded joint was studied, and the optimal parameters of the same material surfacing were obtained. By using the process parameters, the welding test of V groove with free heat treatment was carried out, and the mechanical properties of the welding repair area were verified. The results show that the welding repair process without post-weld heat treatment of 15CrMo steel using the same material is that: firstly use a TIG-R30 welding wire with a diameter of 2.5mm for argon arc welding, then use R307 electrode with a diameter of 3.2mm and welding speed of 150 mm/min for manual arc welding, and remove half-pass welding and air hammer stress-relief treatment during welding. The hardness of the welding repair zone is even better than that of the traditional post-weld heat treatment repair process, which can meet the engineering requirements that the hardness of the welding heat affected zone and the weld zone is not 100HV higher than that of the base metal and the impact energy bigger than 40 J.