Abstract: Rub between rotor and stator is a malfunction in rotor bearing system,and this type of fault can also occur in RMB.A mathematic model of RMB considering the eccentricity of the rotor is established,and the vibrations are analyzed by using bifurcation map,Poincare map and spectrum analysis.The numerical simulation shows that a periodic bifurcation appears in the rotor vibration and the RMB system will become unstable with the increase of the speed and eccentricity.In the spectrum,the order frequencies move from the right to the left near the point of odd multiple frequencies.The study results can be used to control the instability of the RMB system with rub between rotor and stator.And the vibration character of rub can be used to diagnose the fault of rub between rotor and stator of a RMB system.