This paper establishes a dynamic model of the gear system that incorporates the nonlinear oil film force of the sliding bearing and the effects of coupling misalignment excitation. The iterative calculation process is developed utilizing Newmark-β methods and Newton-Raphson methods. The influence of coupling misalignment on the system’s vibration response is investigated. Results indicate that the excitation caused by coupling misalignment significantly affects the dynamic oil film force in the sliding bearing, leading to pronounced vibrations. The misalignment excitation alters the fluctuation frequency of the dynamic oil film force from half of the shaft frequency to double the shaft frequency. The misalignment force exerts a suppressive effect on the oil whirl of the sliding bearing, resulting in a backward shift of its unstable speed. Vibrations generated by coupling misalignment are transmitted to the driving wheel bearing via the driven gear shaft, causing the driving wheel bearing to vibrate at twice the driving wheel shaft frequency. When the sliding bearing does not experience oil whirl and the coupling is properly aligned, the gear pair primarily vibrates at its meshing frequency. When the sliding bearing experiences oil whirl, the dynamic oil film force induces the gear pair to primarily vibrate at half the shaft frequency. In cases of coupling misalignment, the oil whirl of the sliding bearing is suppressed, and the misalignment excitation leads to primary vibrations in the gear pair at double the shaft frequency.