Abstract: The vibration characteristics of faulty multi-span geared rotor system with membrane coupling was modeled and simulated through the FEA (finite element analysis) software ANSYS. The nonlinear dynamic characteristics and responses of the rotor system, and the influences of membrane coupling and gearing on the rotor system were studied according to the change in inherent frequency due to bending-torsioning coupled vibration in the single-span rotor and the whole rotor system when cracks and rubbing fault happen. The results indicated that in such a case the influence on a faulty span is greater than on rests, and the adverse influences of bending vibration and cracks on the rotor system can be weakened or retarded by membrane coupling and gears. What were revealed is beneficial to the fault diagnosis and system maintenance and available to provide reference for designing products.