The predictor-corrector Galerkin method (PCGM) is employed to obtain a lower order system for a two-span rotor-bearing system. First of all, a 32-DOF nonlinear dynamic model is established for the system. Then, the predictor-corrector algorithm based on the Galerkin method is employed to deal with the problem of order reduction for such a complicated system. The first six modes are chosen to be the master subsystem and the following six modes are taken to be the slave subsystem. Finally, the dynamical responses are numerically worked out for the master and slave subsystems using the PCGM, and the results obtained are used to compare with those obtained by using the SGM. It is shown that the PCGM provides a considerable increase in accuracy for a little computational cost in comparison with the SGM in which the first six modes are reserved.