To　simulate　accurately　transport　phenomena　during　laser　keyhole　welding,　a　three-phase　unified　mathematical　model　of　vapor　phase,　liquid　phase　and　solid　phase　was　established　during　laser　deep　penetration　welding.　The　volume-of-fluid　(VOF)　method　was　employed　to　track　free　surfaces.　Roles　of　Fresnel　absorption,　surface　tension,　recoil　pressure,　buoyancy　force　and　gas-liquid　phase　changed　were　considered　in　the　model.　Dynamic　process　of　keyhole　and　molten　pool　and　its　corresponding　temperature　distributions　were　obtained　by　numerical　modeling.　The　laser　keyhole　welding　experiments　on　304　stainless　steel　sheet　show　that　the　computational　results　agree　well　with　experimental　results.