In order to meet the high safety requirement of high-level automatic steering mechanism for commercial vehicle, a kind of steer-by-wire (SBW) system with redundant motors is studied in this paper, and the structure principle and control strategy of the system are studied. Commercial vehicles have the characteristics of large steering resistance moment, which is accompanied by impact and vibration during steering, so the synchronous control of dual motors is the key and difficult problem. Based on the circulating ball steering gear for commercial vehicle, dual-motor synchronous control architecture is designed and the dual-motor global-fast-terminal-sliding-mode (nonsingular-GFTSM) synchronous control is formulated. Compared with the sliding-mode control, the simulation results show that the dual-motor actuator based on nonsingular-GFTSM can better realize the synchronous operation in angle, speed and torque. In addition, a real-time motor fault-diagnosis method based on sliding mode observer and a fault-tolerant control strategy based on smooth switching system are designed, which can achieve fast fault-isolation and smooth torque switching in case of actuator failure in dual-motor system. A Hardware-in-the-Loop (HIL) test bench is built to further verify the effectiveness of the synchronous and fault-tolerance control strategy for dual motors.