According to the nonlinear rotor dynamics theory, a dynamic model that approaches to the practical situation was established for two-span bearing-rotor system with nonlinear oil film. By means of numerical stimulation, the influence of nonlinear oil-film force on the response of rotor system's coupling faults was analyzed. The bifurcation and chaos behaviors of the system were studied under the different work conditions. Nonlinear response diagrams, such as phase plane plots, locus trajectory, as well as amplitude spectrum, were obtained. The complex motion types and their evolvement course of the periodic motion, quasi-periodic motion and chaotic motion were analyzed. The results show that the system of bearing-rotor has abundant nonlinear dynamic behaviors.