In order to realize the stable suspension operation of the magnetic levitation motorized spindle and to meet the requirement of machining precision, the structure and control principle of a certain type of active magnetic levitation motorized spindle are studied. Under the precondition of neglecting the influence of nonlinear factors such as magnetization and flux leakage on the spindle rotor, the stress of the spindle rotor in the magnetic suspension bearing was analyzed. The expressions of magnetic bearing force, bearing air gap offset and control current were established. The critical speed of magnetic suspension motorized spindle system based on incomplete differential Proportion Integration Differentiation (PID) control and the electromagnetic stiffness of magnetic suspension bearing were quantitatively studied. Under different PID control parameters, the bearing stiffness of maglev bearing was obtained, by the curve of degree with vortex frequency and the curve of natural frequency with PID control parameters. The results provide a basis for the further design, application and optimization of the magnetic levitation motorized spindle control system.