In order to study the electronic structure and magnetic properties of the non-rare earth based MnGa binary alloys under isostatic pressure, the crystal structure, formation, spin electronic structure as well as magnetic property of the tetragonal MnGa alloy under isostatic pressure of 500 MPa were systematically studied based on density functional theory calculation method. The results show that the tetragonal MnGa alloy can be formed easier, however the compressibility is anisotropic under the isostatic pressure of 500 MPa. The distances between heterogeneous species are smaller than that between the homogeneous species. The band structures are anisotropic and metallic. The Mn d states form higher net magnetic moment than that of the Ga d states in the MnGa alloy, and the Mn d states contribute to systematic remanent magnetism. The tetragonal MnGa alloy presents weak ferrimagnetism, its net magnetic moment decreases under 500 MPa.