The bearingless permanent magnet synchronous motor （BPMSM） is widely used in industrial production due to the excellent performance of no contact and no wear， However， to achieve accurate control of rotation and suspension， the key is to obtain high-precision rotor position to decouple tangential torque and radial levitation force. To ensure the stable operation of BPMSM in case of position sensor failure， a fault tolerant method of position sensor for BPMSM based on the separation of positive and negative sequence is put forward. First， on the basis of the mathematical model of BPMSM， the influence of sensor failure on the torque and suspension subsystem of the motor is analyzed. On this basis， a fault diagnosis function based on zero crossing detection is proposed to monitor sensor signal faults in real time. Then， rotary coordinate is introduced to analyze the characteristics of positive and negative sequence in single-phase hall signal. Rotor position is calculated by phase-locked loop， which ensure the phase of rotor position is consistent with the positive sequence component separated from hall signal. Fault tolerant system for position detection completed the switch from the fault system to the fault-tolerant control system， realized the normal operation of the BPMSM under sensor fault. Finally， The effectiveness of the proposed method is fully verified by simulation and experiment on a BPMSM prototype.