A　physical　model　coupled　with　heat　transfer　and　fluid　flow　was　developed　to　investigate　the　thermofluid　field　of　molten　pool　and　its　effects　on　SLM　process　of　Inconel　718　alloy,　in　which　a　heat　source　considering　the　porous　properties　of　powder　bed　and　its　reflection　to　laser　beam　is　used.　The　simulation　results　showed　that　surface　tension　caused　by　temperature　gradient　on　the　surface　of　molten　pool　drives　to　Marangoni　convection,　which　makes　fluid　flow　state　mainly　an　outward　convection　during　SLM　process.　Marangoni　convection　includes　convective　and　conductive　heat　flux,　both　of　them　have　effects　of　on　molten　pool　shape,　but　the　effect　of　convective　heat　flux　is　dominant　because　its　magnitude　is　one　order　larger　than　that　of　conductive　heat　flux.　The　convective　heat　flux　accelerates　the　flow　rate　of　the　molten　metal,　benefits　to　heat　dissipation.　The　convective　heat　flux　makes　the　molten　pool　wider,　while　the　conductive　heat　flux　makes　comparably　the　molten　pool　deeper　and　wider.　Furthermore,　heat　accumulation　caused　by　multiple　scanning　increases　convection　and　conduction　heat　flux　resulting　in　the　increase　of　the　width　and　depth　of　the　molten　pool,　but　no　change　of　dominant　role　of　convective　heat　flux　to　the　shape　of　the　molten　pool.