CO2　laser　is　employed　to　join　a　piece　of　powder　metallurgical　material　(PMM)　to　a　stainless　steel　in　butt　joint　welding　mode.　The　powder　Ni35,　as　a　filler　powder,　is　used.　The　weld　metal　comes　from　three　parts　of　stainless　steel,　powder　Ni35,　and　Cu　in　W-Cu　PMM.　It　is　indicated　that　some　parts　of　the　W-Cu　base　metal　are　heated　by　laser　and　the　metal　Cu　at　the　width　of　0.06-0.12　mm　from　the　edge　is　melted　into　the　melting　pool　in　the　laser　welding　process.　The　formation　of　firm　weld　joint　is　just　because　that　the　melting　liquid　metal　could　fill　the　position　occupied　by　metal　Cu　and　surround　the　metal　W　granules　fully.　The　analysis　results　indicate　that　the　mechanism　of　the　laser　welding　for　stainless　steel　and　W-Cu　alloy　is　a　special　mode　of　fusion-brazing　welding.