The invention discloses an LOE (loss of excitation) fault tolerance prediction control method and device for a permanent magnet synchronous motor, and the method comprises the steps: obtaining the rotating speed, voltage and current of the permanent magnet synchronous motor, designing an LOE torque detection sliding-mode observer, obtaining an LOE disturbance estimation value and the observation value of the rotating speed, carrying out the fault tolerance prediction and rotating speed control to calculate a q-axis instruction current, designing an LOE flux linkage detection sliding-mode observer, obtaining a current observation value and a state current observation value after the LOE of a permanent magnet, carrying out the fault tolerance prediction and rotating speed control to calculate an instruction voltage, carrying out the inverse Park transformation and modulation through an SVPWM module, and generating a PWM pulse signal. The device comprises program units corresponding to the steps. The method achieves the quick and no-static-error tracking of the rotating speed and current of the permanent magnet synchronous motor under the LOE condition of the permanent magnet, optimizes the control performances of a rotating speed ring and a current ring, and facilitates the application of the permanent magnet synchronous motor in a severe environment and occasions with higher requirements for reliability.