The　influences　of　the　filler　metal　powder　on　the　intensity　threshold,　weld　formation　and　process　stability　have　been　studied　during　high　power　CO2　laser　welding　of　aluminum　alloy　through　the　comparison　between　welding　with　and　without　metal　powder.　The　experiment　results　demonstrate　that　the　addition　of　the　metal　powder　enhances　the　energy　coupling　efficiency　during　laser　welding　and　reduces　the　power　density　threshold　which　has　been　validated　by　the　testing　data　of　Laserscope　UFF　100.　The　power　density　threshold　of　A2219　can　be　reduce　to　about　50%.　Meanwhile,　the　pictures　collected　by　the　high　speed　camera　indicate　that　the　addition　of　the　metal　powder　weakens　the　fluctuation　of　the　laser-induced　plasma　and　keeps　the　plasma　stabilizing　above　the　workpiece.　So　a　stable　welding　process　and　well-formed　weld　can　be　obtained　in　a　relatively　easy　way.