At present, the current ripple is usually used as the demodulation signal in the selfsensing shaft displacement detection technology of magnetic bearings. However, this method has a strong dependence on the quality of the ripple. The analytical formula is more complex, and the sampling requirements of the controller are higher. To improve the detection accuracy of the self-sensing shaft displacement of magnetic bearings, a periodic peak current demodulation method is proposed based on the buck chopper circuit. Firstly, the high frequency pulse width modulation voltage is input to the magnetic pole coil of the magnetic bearing. The nonlinear relationship between the peak current and the coil inductance in a single current cycle of the high-frequency pulse width signal is established. Then, the Newton-Raphson method is used to iterate the nonlinear values of the relationship. Finally, the displacement of the magnetic bearing rotor is calculated by combining the iterative results with the inductance formula of the magnetic pole coil of the magnetic bearing. Simulation and experiments show that the dynamic self-sensing rotor displacement real-time detection of the magnetic bearing controller can effectively track the rotor displacement detection signal of the eddy current sensor. The displacement fluctuation error of the two is less than the minimum error required by the magnetic bearing suspension control. In the displacement demodulation experiment of 0.8 mm air gap, when 5~15 kHz high-frequency pulse width modulation voltage with different voltage amplitudes is used as the self-sensing detection signal of the magnetic bearing rotor, the error between the static self-sensing rotor displacement demodulation value of all detection signals and the static demodulation displacement value of eddy current sensor is within the controllable range. When 10 kHz high-frequency pulse width modulation voltage is used as the detection signal, the maximum error between the static self-sensing displacement demodulation value of magnetic bearing and the static displacement demodulation displacement value of the eddy current sensor is not more than 24.7 μm, and the minimum is 0.9 μm.