Abstract: The manufacturing of a heavy type bevel gear shaft is generally machined separately, and then jointed by welding. Aimed to the joining of the quenched and tempered 42CrMo steel bevel gear shafts for a heavy-duty machine, a 3500 W Slab CO₂ laser was applied and narrow gap laser welding process was adopted with filler wire of TGS -2CM.Meanwhile, the performance and metallographic structure of the joint were studied.The experiment results demonstrate that there are no cracks and porosities in the joint even without preheating and postweld heat treatment when the appropriate laser welding parameters are used.The microstructure in the weld and heat-affected zone is fine bainite.The micro-hardness of fusion area is about 580HV0.2, and no apparent softened zone exists in the welded joint.The tensile strength of the joint is in 980-1080 MPa, and equivalent to that of the base material, which is satisfied with the service demand.