Most　of　the　laser　welding　defects　are　likely　to　be　related　to　the　welding　process　transport　phenomena　induced　by　the　energy　conversion　process　in　the　keyhole.　The　keyhole　wall　is　the　interaction　interface　between　the　laser　and　welded　material,　and　studying　its　micro-morphology　is　significant　for　understanding　the　energy　conversion　process.　Because　the　current　measuring　methods　are　limited,　observation　of　keyhole　wall　micro-morphology　is　still　a　challenge.　In　this　paper,　a　novel　method　was　designed.　The　keyhole　wall　was　preserved　as　the　high-power　fiber　laser　was　suddenly　shut　off　during　welding　process,　and　then　it　was　measured　by　using　a　scanning　electron　microscopy　(SEM).　The　results　show　that　the　laser　beam　directly　acted　on　the　keyhole　front　wall　during　welding.　The　concentric　elliptical　rings,　wrinkles,　and　ripples　were　found　on　the　laser-action　region.　These　micromorphologies　indicate　that　the　energy　coupling　is　mainly　the　absorption　of　the　keyhole　front　wall,　and　the　keyhole　formation　is　similar　to　a　laser　drilling　on　the　keyhole　front　wall　during　welding.　The　novel　method　can　be　used　to　investigate　on　the　formation　of　the　welding　defects　during　high-power　fiber　laser　welding　in　the　future　study.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.