Considering the influence of multi?source excitations induced by unbalanced mass，sealing fluid，bearing oil film，and base vibrations，the dynamic model of a rotor system was established applying the Lagrange approach. Adopting the Runge?Kutta method，the nonlinear state equation was solved. By means of frequency spectrum，bifurcation diagram and rotor trajectories，the dynamic behaviors of the system were analyzed. In addition，the vibration level of rotor system was studied by rotational speed?vibration intensity curves. The influences of base vibration on the nonlinear dynamic properties and instability threshold of rotor system were comparatively analyzed. And the effects of different forms of base vibration and its frequency and amplitude variation on the dynamic characteristics and vibration responses of the rotor system were studied. It is found that the stability of the system is reduced by base vibration. The impacts of base vibrations on the dynamics of the rotor system show clear directionality.