Active magnetic bearings enable greater spindle dynamic stiffness through higher attainable bearing surface speeds. However, the active magnetic bearing system is highly nonlinear due to the interaction between electromagnetic field and rotor dynamics. Its nonlinear character becomes prominent when rotating in high speed. The operation undergoes route-to-chaos and is vulnerable to external excitation, which eventually leads to detrimental failure. A novel simultaneous time-frequency control theory is developed for controlling the active magnetic bearing at high speed. The control theory is able to tolerate the uncertainties in the system due to on-line identification and the deterioration in both time and frequency domain can be restrained.