In　this　paper,　Ti6Al4V　octahedron　lattice　structures　with　top　cap　and　bottom　base　were　fabricated　through　selective　laser　melting　(SLM).　The　structural　integrity,　microstructural　evolution,　compressive　properties　and　failure　mechanism　of　as-fabricated　(AF)　and　vacuum　annealing　treated　(VAT)　samples　were　studied　through　both　experiments　and　numerical　modeling.　The　X-ray　computed　tomography　analysis　revealed　that　vacuum　annealing　had　an　insignificant　effect　on　internal　pore　elimination　and　porosity　reduction.　For　both　the　AF　and　VAT　samples,　larger　pores　exhibited　more　irregular　shape　than　smaller　pores.　The　microstructural　analysis　suggested　that　vacuum　annealing　was　able　to　transform　acicular　α/α`　martensites　into　uniformly　distributed　lamellar　α　+　β　phases　and　also　to　cause　the　formation　of　nano-particle　precipitation　and　dislocation.　The　compressive　test　indicted　that　the　lattice　structure　with　confined　top　and　bottom　had　much　better　compressive　properties　than　those　without.　Also,　vacuum　annealing　significantly　improved　the　compressive　strength　by　26%　due　to　the　synergistic　effect　of　residual　stress　relief,　nano-particle　precipitation　and　dislocation　strengthening.　The　ductility　of　the　VAT　sample　was　also　improved　as　compared　to　the　AF　sample,　which　was　mainly　attributed　to　the　formation　of　α　+　β　phases.　©　2020　The　Authors