The　paper　comparatively　investigates　the　microstructures　and　mechanical　properties　of　Inconel　718　superalloy　manufactured　by　selective　laser　melting　(SLM)　and　casting.　The　finite　element　analysis　(FEA)　method　is　used　to　simulate　the　temperature　fields　during　SLM　and　casting　processes.　Driven　by　ultra-high　temperature　gradient　and　ultra-fast　cooling　rate　during　SLM　process,　the　fine　grains　(average　grain　size　of　48　mu　m)　and　dispersed　fine　precipitation　in　SLM-ed　sample　even　after　HSA　(homogenization　+　solution　+　aging)　and　HA　(homogenization　+　aging)　heat　treatment　significantly　enhance　its　mechanical　properties,　which　far　exceeds　that　of　casting　with　average　grain　size　of　1300　mu　m,　and　is　comparable　to　that　of　forging.　The　microstructure　of　casting　with　coarse　irregular　Laves　phases,　acicular　delta　precipitates　and　globular　carbides　in　the　interdendritic　zones　after　HSA　heat　treatment　and　some　defects　existed　possibly　result　in　premature　failure　of　tensile　samples.　The　microstructure　without　delta　phases　but　only　some　globular　carbides　in　the　grain　boundary　of　SLM-ed　sample　after　HA　heat　treatment　possesses　higher　mechanical　properties　than　that　after　HSA　heat　treatment,　in　which　there　is　only　some　finer　needle-like　delta　phase　and　few　carbides　are　precipitated　in　the　grain　boundaries.　The　analysis　shows　the　large　amounts　of　delta　phase　precipitated　in　the　matrix　will　deteriorate　the　plasticity　of　SLM-ed　IN718　superalloy,　the　appropriate　reduction　of　the　delta　phase　will　improve　the　strength　and　plasticity　of　material　simultaneously.