Abstract: An experimental setup was developed to investigate nonlinear vibration characteristics of rotor bearing system with rub-impact fault. It is found that in a system where the effect of oil film force is comparatively small, the rub-impact action will cause the system to form sub-and super-harmonic vibration components, whereas in a system supported by sliding bearings a lot of super-harmonic vibration components will form because the very thin clearance between rotor and stator causes them to rub and impact each other before oil film whirl. In case the clearance is comparatively thick, they will rub and impact each other after oil film whirl and the rub-impact effect will be very small on the system at that moment with a maximum effect of oil film force in bearing on the system.