In　order　to　simulate　accurately　the　formation　process　of　the　keyhole　in　laser　deep　penetration　welding.　Multiple　reflection　and　Fresnel　absorption　are　implemented　simultaneously　with　the　ray　tracing　technique　in　the　keyhole.　With　all　the　governing　equations　including　continuity,　momentum　and　energy　equation,　the　VOF　method　is　adopted　to　trace　the　free　surface　of　the　molten　pool.　Simulation　results　are　compared　with　the　experimental　ones　to　verify　its　validity.