In order to overcome the nonlinear influence of electromagnet material on control system, a new method of nonlinear power amplifier was put forward. By this special amplifier, the differential electromagnet load system became a linear system. For the controller of active suspension, the control object was transformed into a linear control system, which facilitated the real-time calculation of the controls variable. The experiment result showed that the nonlinear amplifier had expanded the dynamic range of the controller and improved the stability of the active magnetic levitation control system.