The invention provides a facing machine for a steel tube. A common lathe cannot clamp the large-caliber steel tube. The facing machine comprises a supporting frame, a milling device, a lifting device, a moving device and a rotating device. The milling device comprises a driving motor and a machine head, and is provided with a sliding block. The lifting device comprises a guiding rod, a lifting motor and a screw rod, wherein the guiding rod penetrates the milling device, the screw rod is connected with the lifting motor, and the screw rod is in threaded fit with the sliding block of the milling device. The rotating device is fixed to the supporting frame. The moving device is connected with the rotating device. The machine head comprises an installation seat and cutters. The installation seat is provided with a plurality of installation grooves annularly arranged along the surface of the installation seat, the cutters are installed in the installation grooves, and chip grooves are formed in the installation seat. The steel tube facing machine is simple in structure, reasonable in design, wide in application range, high in working efficiency and convenient to operate.