Selective　Laser　Melting　(SLM)　was　used　to　fabricate　Erbium-modified　AlSi7Mg　alloy.　The　work　aims　to　investigate　the　effects　of　laser　volumetric　energy　density　and　focus　shift　on　surface　quality,　internal　defects　and　microstructure　during　the　SLM　process.　Based　on　the　optimized　process　parameters,　the　effect　of　rare　earth　element　Er　to　AlSi7Mg　alloy　on　its　microstructure　and　mechanical　properties　were　studied.　With　a　raise　of　volumetric　energy　density,　the　size　of　aluminum　sub-cells　increases,　and　the　high　energy　density　promotes　the　in　situ　precipitation　of　supersaturated　silicon　elements　in　the　form　of　dispersed　silicon　particles.　It　was　thought　that　the　laser　focus　shift　could　change　the　energy　density　and　the　molten　pool　size,　which　affected　the　internal　defects　and　the　size　of　sub-cells　plus　eutectic　silicon　particles.　The　alloy　(A357　+　0.2Er　wt.%)　fabricated　by　SLM　was　operating　with　the　optimized　processing　parameters,　then　a　small　amount　of　equiaxed　grains　were　formed　at　the　boundary　of　the　molten　pool,　which　would　promote　the　refinement　of　columnar　grains　and　improve　the　mechanical　properties.　Meanwhile,　the　yield　strength　was　297　MPa,　the　tensile　strength　was　441　MPa　and　the　elongation　was　8%.