The proper orthogonal decomposition （POD） method is used to model the shell-motor-rotor coupled system with bearing nonlinearities to reduce the computational cost. The rotor system with 192 degrees of freedom is modeled by the finite element method for the coupled shell-motor-rotor structure. The basic principle of the POD method and its specific expression in the shell-motor-rotor coupled system are introduced. By using the POD method， the shell-motor-rotor coupled system is reduced to 20， 18 and 15 degrees of freedom， and the computation time is reduced by more than 94%. The time course curves and spectra of the simplified system and the original system are compared， which verifies the efficiency and accuracy of the POD method.