The invention discloses a full-automatic combination machine for processing a crankshaft of an engine. The full-automatic combination machine comprises a processing table, positioning blocks are symmetrically and fixedly connected to the top of the processing table, a bearing plate is connected between two positioning blocks in a sliding manner, a ball body is rotationally embedded in the bearingplate, a first connecting rod is fixedly connected to the top of one ball body, the top of the outer wall of the first connecting rod is sleeved with a connecting sleeve in a sliding manner, a first arc plate is fixedly connected to the top of the connecting sleeve, a second arc plate is rotationally connected to the top of the first arc plate, polishing plates are fixedly connected to one sides,opposite to each other, of the first arc plate and the second arc plate correspondingly, and supporting columns are arranged on two sides of the top of the processing table. By using the arrangement way of the first arc plate and the second arc plate, a ring can be formed by the first arc plate and the second arc plate, and sleeves the outer wall of the crankshaft, and the crankshaft rotates alongwith the ring when the ring rotates, so that the polishing plates polish the crankshaft, which improves the crankshaft polishing efficiency.