The　shape　of　welding　pool　in　laser　deep　penetration　welding　was　calculated　based　on　continuity　equation,　momentum　conservation　equation　and　energy　conservation　equation　using　FLUENT　solver.　Solidification/Melting　model　and　κ-Ε　model　were　used.　Simulation　results　showed　that　the　recoil　pressure　on　the　front　wall　of　the　keyhole　is　an　important　driving　force　of　welding　pool　fluid　flow　because　of　large　temperature　gradient　in　the　front　part.　The　larger　size　of　the　solidification　transition　zone　of　welding　pool　in　the　liquid-solid　interface　was　related　to　solidification　heat.