<p>To investigate the influence of waves and traffic flow on the vibration of large-span bridges, a vibration response model considering the combined action of wave–vehicle–bridge was developed. Based on the existing Coupled Euler–Lagrange (CEL) methods, a new simplified analytical approach that takes into account the effects of water flow was proposed. Using a cable-stayed bridge as the case study, three models were developed: the vehicle–bridge coupling model without the wave effect, the vehicle–bridge coupling model with the wave effect, and the wave–vehicle–bridge simplified model with the wave effect. In addition, to simplify the model, a simplified method is proposed which considers the equivalent wave force as an actual wave. A comparative analysis was conducted to evaluate the differences in the mid-span vertical displacement, transverse displacement, and vertical acceleration under the wave and no-wave conditions. The computational accuracy of the proposed simplified method is compared with that of the conventional CEL approach. The results demonstrate that waves significantly affect the vertical displacement, transverse displacement, vertical acceleration, and longitudinal displacement. The coefficient of determination (<i>R</i>²) of each measurement point is consistently above 0.91, indicating that the simplified analysis method achieves high accuracy for simulating the wave effects.</p>