The　effect　of　heat　treatment　on　the　microstructure　and　high　temperature　mechanical　properties　of　SLM　GH4169　alloy　was　studied　by　using　a　self-developed　in-situ　high　temperature　tensile　device.　The　results　show　that　the　grain　morphology　of　as-built　alloy　changes　from　columnar　crystal　to　equiaxed　crystal　after　homogenization+solid　solution+aging　treatment　（HSA）　，　coupling　with　Laves　phase　dissolution，　and　a　large　amount　of　γ′　and　γ″　strengthening　phase　precipitates.　At　650　℃，　the　yield　strength　and　tensile　strength　of　the　as-built　sample　are　574　MPa　and　740　MPa，　while　the　yield　strength　and　tensile　strength　of　HSA　sample　are　818　MPa　and　892　MPa　respectively，　which　are　42.5%　and　20.1%　higher　than　that　of　the　deposited　alloy.　The　deformation　process　can　be　further　characterized　by　in-situ　tensile　testing.　The　surface　grain　undulation　of　the　as-built　sample　gets　larger，　the　coordinated　deformation　ability　becomes　stronger，　and　the　plastic　flow　ability　gets　better.The　cracks　in　the　as-built　sample　are　originated　around　the　Laves　phase，　spreading　along　the　dendrite　towards　the　maximum　shear　stress，　and　shear　fracture　occurs　after　necking　of　the　sample.　In　HSA　samples，　the　cracks　are　initiated　around　carbides　and　propagating　along　the　grain　boundaries.　The　fracture　mode　is　a　mixed　type，　involving　both　intergranular　and　transgranular　fractures.　©　2024　Chinese　Journal　of　Aeronautics.　All　rights　reserved.