Abstract: For the welding repair of broken 37SiMn2MoV steel gear shaft, the combined welding repair technology of small size shaft head inserted into shaft body with interference fitting and U groove shielded metal arc welding of shaft head and shaft body was used. The welding difficulty of 37SiMn2MoV steel was analyzed, by correctly selecting the type of welding rod and joint form, arranging the transition layer, filling layer and cover layer reasonably, strictly controlling the preheating, post-heating and interlayer temperatures, and carrying out the small line energy welding, good welding repair effect has been obtained.