Under complex dynamic loads, the motions of the rotor and bending of the shaft can make the inner and outer races being of support bearings nonparallel in the rotor-bearing system, which will significantly affect the contact performance between the roller and race of support bearings. In this study, a rotor-bearing system with a cantilevered pinion is established by coupling the kinematic equations of the rotor with the determination of deflection deformation of the shaft. The time-varying mesh stiffness of gear pair, interactions between the roller and race of support bearings, and dynamic forces induced by dynamic rotor eccentricity are comprehensively considered in this model. In addition, a spatial rolling bearing dynamics model considering the radial load distribution along width and flexible roller is especially involved in this dynamic system using the slice method. The effect of traction torque, rotor eccentricity, and external excitation is analyzed. The results indicate that the non-uniform loads induced by gear engagement, dynamic rotor eccentricity, and external excitation will lead to local fatigue failures for support bearings. The fatigue lives of bearings are significantly lower than those calculated based on the static loads. Taking the traction motor of a railway locomotive as an example, this study is proven to be capable to provide a more reasonable method to investigate the service conditions of rolling bearings and assess the corresponding fatigue lives.