Geometry,　formation,　electronic　structure　as　well　as　magnetic　properties　of　the　tetragonal　MnGa　alloy　were　systematically　studied　by　density　functional　theory　method.　The　results　show　that　the　tetragonal　MnGa　has　formation　enthalpy　of　-4.85　eV,　which　is　slightly　higher　than　other　compounds　without　d　state　electrons.　It　has　conductor　like　band　structure　with　the　deep　valance　bands　formed　by　d　state　electrons,　they　show　strong　localization　effect.　The　tetragonal　MnGa　alloy　shows　obvious　spin　polarization.　The　s　state　electrons　near　Fermi　energy　and　the　p　state　electrons　under　Fermi　energy　have　weak　spin　polarization,　the　d　state　electrons　which　form　conductor　band　and　bands　below　Fermi　energy　have　strong　spin　polarization,　they　contribute　to　the　total　electronic　as　well　as　magnetic　properties.　The　s　and　p　state　electrons　of　Mn　have　weak　spin　polarization,　its　d　electrons　which　form　conductor　band　and　bands　below　Fermi　energy　have　strongest　spin　polarization.　The　d　electrons　of　Ga　which　form　bands　below　Fermi　energy　have　weak　spin　polarization.　The　two　kinds　of　Ga　have　different　spin　polarization　states.　The　tetragonal　MnGa　alloy　has　net　magnetic　moment,　it　shows　weak　ferrimagnetism.　©　2022,　Journal　of　Synthetic　Crystals　Press.　All　right　reserved.