The　study　of　molten　pool　characteristics　is　a　powerful　means　of　determining　the　quality　of　laser　additive　manufacturing　forming.　In　this　paper,　a　three-dimensional　transient　thermal　flow　field　numerical　model　of　Ti6Al4V　powder　processed　by　LPBF　is　developed　based　on　FLOW-3D　soft-ware,　and　the　dynamic　evolution　of　the　molten　pool　with　fixed　process　parameters　is　quantita-tively　described　using　dimensionless　numbers　in　computational　fluid　dynamics.　It　is　shown　that　the　main　heat　transfer　mode　of　the　molten　pool　is　thermal　convection;　the　evaporative　back　sitting　pressure,　surface　tension　and　Marangoni　shear　force　are　the　main　driving　forces　for　the　evolution　of　the　molten　pool.　Furthermore,　the　influence　of　key　process　parameters　on　the　heat　flow　field　of　the　molten　pool　was　analyzed.　When　the　laser　power　was　300　W,　the　depression　depth　and　molten　pool　depth　caused　by　the　recoil　pressure　were　significantly　larger,　and　the　isothermal　density　of　the　solidification　region　was　more　intensive;　when　the　scanning　speed　was　increased　from　0.4　m/s　to　0.8　m/s,　the　molten　pool　length　was　reduced　from　524　&　mu;m　to　410　&　mu;m,　and　the　line　energy　density　was　reduced　making　the　amount　of　melted　powder　decrease.　The　wettability　and　fluidity　of　the　molten　state　metal　becomes　worse;　when　the　scanning　interval　increases　to　120　&　mu;m,　a　large　number　of　incompletely　melted　powder　tracks　cannot　lap　correctly　at　the　midline　of　the　double　track.　The　results　of　the　above　simulations　achieve　a　high　degree　of　agreement　with　the　surface　quality　of　the　specimens　during　the　experiments,　which　provides　guidance　for　quantitative　analysis　of　molten　pool　evolution　and　prediction　of　Ti6Al4V　forming　quality.