High　entropy　alloys　(HEAs)　have　excellent　mechanical　properties　for　wide　application　range　and　market　demand.　However,　low　ductility　is　a　persistent　problem　with　such　alloys.　With　two　different　protective　gases　(Argon　and　Nitrogen),　a　new　type　of　high　entropy　alloy　CoCr2.5FeNi2TiW0.5　has　been　prepared　by　selective　laser　melting　(SLM)　technology　for　additive　manufacturing　with　discussion　and　analysis　on　the　influence　of　microstructure　and　mechanical　properties　in　this　paper.　Under　the　protection　of　argon　(Ar),　the　HEA　forms　a　single-phase　solid　solution.　Meanwhile,　the　second　phase　TiN　is　formed　when　nitrogen　(N2)　is　used　as　protective　gas,　which　eventually　becomes　the　matrix　body-centered　cubic　(BCC)　with　precipitates　TiN.　The　average　microhardness　values　of　samples　under　the　protection　of　Ar　and　N2　were　436.7HV　and　499.2HV,　respectively.　Along　the　scanning　direction,　the　SLM　sample　(N2　protection)　shows　higher　properties　on　the　average　yield　strength　(YS),　ultimate　tensile　strength　(UTS),　and　average　elongation　of　samples　(581　MPa,　893　MPa,　and　9.9%,　respectively.),　compared　with　those　obtained　under　Ar　atmosphere.　This　method　could　effectively　refine　grain　structure　and　offer　theoretical　guidance　to　manufacture　fine　grain　materials　with　high　strength　and　ductility　of　new　HEA　components.　©　2021　Elsevier　B.V.