A　mathematical　model　that　is　capable　of　simulating　the　fluid　flow　and　heat　transfer　during　fully　penetration　laser　welding　is　developed　to　study:　the　shape　of　the　keyhole　and　its　stability;　velocity　vectors　and　distribution　in　the　weld　pool.　Firstly,　a　new　combination　heat　source　model　consisting　of　a　rotary　Gaussian　volumetric　heat　source　and　a　double　ellipsoidal　volumetric　heat　source　during　laser　keyhole　welding　is　developed.　It　represents　substantial　characteristic　of　heat　transfer　of　the　keyhole.　Secondly,　A　mathematical　model　for　the　simulation　of　heat　transfer　and　fluid　flow　in　weld　pool　phenomena　during　deep　penetration　laser　beam　welding　based　on　a　numerical　solution　of　the　conservation　equations　of　energy,　momentum　and　mass　is　presented.　and　verification　and　validation　tests　were　carried　out.