The　manufacture　of　heavy　type　bevel　gear　shafts　is　generally　machined　separately,　and　then　jointed　by　welding.　Aimed　to　the　joining　of　quenched　and　tempered　42CrMo　bevel　gear　shafts　for　heavy-duty　machine,　a　3500　W　Slab　CO　2　laser　was　applied　and　narrow　gap　laser　welding　process　was　adopted　with　filler　wire　of　TGS-2CM,　at　the　same　time,　the　performance　and　metallographic　structure　of　the　joint　were　studied.　The　experimental　results　demonstrate　that　there　are　no　cracks　in　the　joint　even　without　preheating　and　post-weld　heat　treatment　when　the　appropriate　processing　parameters　are　used.　The　microstructure　of　the　weld　bead　and　heat-affected　zone　is　fine　bainite.　The　micro-hardness　of　fusion　area　is　about　HV0.1530,　and　no　apparent　softened　zone　exists　in　the　welding　joint.　The　average　tensile　strength　value　of　the　joint　is　1020　MPa,　equivalent　to　that　of　the　base　material,　which　is　satisfied　with　the　service　demand.　Currently,　the　actual　welding　products　were　already　used　in　industry.