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.