Abstract: A computer mainframe housing, of which the main materials are made in flat shapes from steel sheets with plastic directly molded thereon through the process of injection molding, including a back panel, two identical cover panels with one for the top and the other for the bottom, two identical side panels with one for the left and the other for the right, a partition board, a plurality of master board mounting plates, a main disk drive case, an auxiliary disk drive case, a front panel connected with other parts by retaining devices thereon, the front panel having a square window with a square control panel detachably mounted thereon, the main disk drive case having a square front face, the hole into which the main disk drive case is inserted, being made in the shape of a square, wherein the steel sheets of the materials provide good shielding effect against magnetic waves; the front, back, side, and cover panels can be piled up together to reduce space occupation before assembly; retaining devices are directl