Abstract: In order to investigate the mechanism of rain-wind-induced vibrations (RWIV), a series of 2-dimensional CFD models of stay cables with fixed upper rivulets were computed to obtain the curves of aerodynamic coefficients vs. the positions of upper rivulets. The influence on cable aerodynamic characteristics caused by the upper rivulet was analyzed. Correspondingly, a 2-dimensional 2DOF model of RWIV was established and a numerical program employing the curves from CFD computation achieved the complete computer-based stimulation of RWIV. By contrast with the results from an artificial rainfall wind tunnel test, the mean wind velocity and turbulence intensity were studied based on the numerical stimulation. The study shows that the oscillation of the upper rivulet is the reason causing RMIV. The simulation results also indicate that the response of the stay cable in RWIV is close to that of wind tunnel test results when the fluctuating wind is considered.