This paper focuses on rotor dynamic analysis of the magnetic levitation based high-speed electrical machine. Firstly, the dynamic model of the magnetic levitation rotor is established and the support stiffness of the magnetic bearings is calculated. Furthermore, the rotor system's dynamic analysis with ANSYS software is implemented with the assumption that magnetic bearing is considered as a certain stiffness of spring model. Finally, the rotor system's vibration modes and critical speeds are obtained. The analytical result not only provides a theoretical support for safe operation of the rotor system and going through the lower order critical speed control, but also gives important reference for the structure design and optimization of the rotor.