The disturbance rejection control system for 5 degree-of-freedom (DOF) magnetic bearing was designed based on proportion-integration-differentiation (PID) control combined with disturbance rejection process. Through analysis of the rotor motion model

a more accurate disturbance observer model of magnetic bearing was revised and obtained. The stability analysis of the discrete disturbance observer was conducted and the parameter tuning method was elaborated

making the parameter tuning process of disturbance observer more normative and convenient. The experimental results show that: when the disturbance rejection control is employed in PID control

displacement fluctuations of rotor disturbed DOFs are reduced by 38.7% and 67% respectively

and the motion track fluctuation of the rotor axis center is reduced by 21% with rotating speed of 20000r/min

thus verifying the superiority of the disturbance rejection control compared with PID control.