Abstract: When open-circuit faults occur in the multi-phase permanent magnetic synchronous motor (PMSM), the current distortion and internal parameters variation of motor cause unpredictable disturbances to the system, which brings a challenge to the stable sensorless operation. To realize the online transition of fault tolerant control, this paper proposes a sensorless fault tolerant strategy of the multi-phase PMSM based on axes transformation. First, the reducing-order decoupled model of the postfault multi-phase PMSM is established using axes transformation. And postfault currents are refactored to guarantee the maximum torque output. The modeling approach applies to arbitrary open-circuit faults of the multi-phase PMSM. Also, the obtained mathematical model and current references would not vary with fault phase locations. On this basis, the modified sliding mode observer is established by the reducing-order decoupled model based on axes transformation, which improves the accuracy of rotor position estimation in the sensorless fault tolerant system. Finally, the effectiveness of the proposed control strategy is verified by open-circuit fault tolerant experiments with a 9 kW nine-phase PMSM.