A　high-temperature　in-situ　tensile　stage　setup　developed　by　the　authors　was　combined　with　electron　backscatter　diffraction　(EBSD)　to　study　the　microstructural　evolution　behavior　of　Ti-6Al-4V　alloy　produced　by　laser　direct　melting　deposition　(LDMD)　at　400　degrees　C.　This　technique　provided　direct　observation　of　the　microstructure　evolution　and　deformation　behavior　of　materials　under　dynamic　tensile　loading　at　operating　temperature.　The　evolution　of　grain　morphology,　misorientation　angles　of　grain　boundaries,　and　Schmid　factor　(SF)　were　systematically　investigated.　The　results　indicated　that　the　grains　no　longer　sustained　the　initial　lamellar　morphology　and　underwent　a　severe　microstructural　evolution　during　plastic　deformation.　Various　grain　morphologies　were　observed　at　different　tensile　strain　levels.　The　statistical　analysis　revealed　the　reduction　of　high-angle　grain　boundaries＇　(HAGBs)　fraction　among　alpha/alpha　grains,　with　the　opposite　trend　for　low-angle　grain　boundaries　(LAGBs).　The　increased　Schmid　factor　values　(SF　11-20　11-20　11-20　slip　system　exhibited　a　sharp　drop　to　SF　＞　0.4　at　higher　strain　levels.　Moreover,　it　was　observed　that　high-SF　grains　changed　their　orientations,　while　low-SF　ones　split　into　smaller　grains　under　tensile　load.　The　kernel　average　misorientation　(KAM)　maps　showed　that　deformation　promoted　dislocation　motion,　generating　many　LAGBs.　The　increasing　number　of　LAGBs　and　slip　openings　reduced　the　boundary　resistance　and　provided　an　easy　path　to　detour　the　main　crack　propagation　in　response　to　the　applied　stress,　while　the　LDMD　Ti-6Al-4V　specimen　showed　ductile　fracture　behavior.