The　keyhole　formed　during　laser　deep　penetration　welding　significantly　improves　laser　energy　efficiency.　However,　this　process　involves　complex　interactions　of　multiphase,　making　it　susceptible　to　welding　defects　like　spattering　and　porosity.　In-situ　monitoring　during　welding　can　help　identify　key　factors　influencing　welding　stability.　Nevertheless,　current　monitoring　methods　have　limitations　that　prevent　establishing　a　clear　relationship　between　the　vapor　plume　and　the　keyhole　for　accurate　welding　mode　identification.　To　address　these　challenges,　this　study　introduces　a　novel　real-time　multimode　in-situ　monitoring　technology　that　combines　ultrafast　synchrotron　radiation　imaging　with　high-speed　visible　light　imaging,　allowing　simultaneous　observation　of　multiphase　dynamics　during　laser　welding.　The　research　establishes　a　connection　between　the　internal　keyhole　and　the　surface　vapor　plume　evolution　in　metals.　It　also　finds　that　vapor　plume　fluctuations　indicate　keyhole　mode　transition,　challenging　the　traditional　belief　that　bright　vapor　plume　emergence　signifies　this　transition.　Additionally,　the　study　observes　keyhole　oscillation　frequency　ranging　from　3.75　kHz　to　7.5　kHz,　with　the　frequency　increasing　as　laser　power　rises.