In　order　to　track　the　free　interface　of　the　melt　pool　and　understand　the　evolution　of　the　melt　pool,　the　flow　of　fluid,　and　the　interface　behavior　of　gas　and　liquid,　a　physical　model　is　developed　by　using　the　VOF　method　in　this　paper.　Its　characteristics　are　a　combined　heat　source　model,　including　a　parabolic　rotation　and　a　cylindrical　distribution,　and　a　powder　bed　stochastic　distributed　model　with　powder　particle　size.　The　unit　interface　between　the　metallic　and　gas　phase　in　the　laser-powder　interaction　zone　can　only　be　loaded　by　the　heat　source.　Only　the　first　and　second　laser　scanning　tracks　are　simulated　to　reduce　the　calculation　time.　The　simulation　results　show　that　process　parameters　such　as　laser　power　and　scanning　speed　have　significant　effects　on　the　fluid　flow　and　surface　morphology　in　the　melt　pool,　which　are　in　good　agreement　with　the　experimental　results.　Compared　with　the　first　track,　the　second　track　has　larger　melt　pool　geometry,　higher　melt　temperature,　and　faster　fluid　flow.　The　melt　flows　intensely　at　the　initial　position　due　to　the　high　flow　rate　in　the　limited　melt　space.　Because　there　is　enough　space　for　the　metal　flow,　the　second　track　can　obtain　smooth　surface　morphology　more　easily　compared　to　the　first　track.　The　melt　pool　temperature　at　the　laser　beam　center　fluctuates　during　the　laser　scanning　process.　This　depends　on　the　effects　of　the　interaction　between　heat　conduction　or　heat　accumulation　or　the　interaction　between　heat　accumulation　and　violent　fluid　flow.　The　temperature　distribution　and　fluid　flow　in　the　melt　pool　benefit　the　analysis　and　understanding　of　the　evolution　mechanism　of　the　melt　pool　geometry　and　surface　topography　and　further　allow　regulation　of　the　L-PBF　process　of　Ti6Al4V.