Powder　metallurgy　possesses　the　advantages　of　low　energy　consumption,　less　material　consumption,　uniform　composition,　and　near-final　forming.　In　order　to　improve　the　mechanical　properties　and　high-temperature　oxidation　resistance　of　CoCrNi　medium-entropy　alloy　(MEA),　CoCrNiAlX　(X　=　0,　0.1,　0.3,　0.5,　0.7)　MEAs　were　prepared　using　mechanical　alloying　(MA)　and　spark-plasma　sintering　(SPS).　The　effect　of　aluminum　content　on　the　microstructure　and　properties　of　the　MEAs　was　investigated.　The　results　show　that　the　CoCrNi　MEA　is　composed　of　face　center　cubic　(fcc)　phase　and　some　carbides　(Cr23C6).　With　the　increase　in　Al　content,　there　exists　Al2O3　precipitation.　When　the　Al　content　is　increased　to　Al-0.5　and　Al-0.7,　the　body　center　cubic　(bcc)　phase　begins　to　precipitate.　The　addition　of　aluminum　significantly　enhances　the　properties　of　the　alloys,　especially　those　containing　fcc+bcc　dual-phase　solid　solutions.　The　yield　strength,　compressive　strength,　and　hardness　of　CoCrNiAl0.7　alloy　are　as　high　as　2083　MPa,　2498　MPa,　and　646　HV,　respectively.　The　high-temperature　resistance　also　reaches　the　oxidation　resistance　level.　Different　oxides　include　Cr2O3,　Al2O3,　and　(Co,　Ni)　Cr2O4　and　NiCrO3　spinel　oxides　formed　on　the　surface　of　alloys.　The　formation　of　an　Al2O3　oxidation　film　prevents　the　further　erosion　of　the　matrix　by　oxygen　elements.