Based on the research of nonlinear Maglev system's Hopf bifurcation, one factor which leads to the system vibrations,was studied by analyzing the connection between the cascade PID parameters and the periodic motion.The cascade PID control arithmetic was given,the four rank system dynamic model was constructed,the stability range of the control parameters was deduced,and the condition of the Hopf bifurcation was proved. We got the reduced two rank model using the center manifold theorem,and obtained the stability of the Hopf point and the corresponding vibration frequency of the limit circle with PB normal form. The result shows that the Maglev system based on the cascade PID controller has one unstable Hopf bifurcation point,and the system vibrates in 5～7Hz,which will emanate eventually.