Abstract: According to the soakage theory and Prandtl boundary layer theory, the interactive force model between the cable surface and the rivulet is proposed for analyzing the rain-wind-induced vibration of stay cables. In addition to the well-known viscous damping force, the proposed force model includes the Coulomb damping force which accounts for the effect of water soakage on materials of cable surface. Equations of motion of the coupled cable-rivulet system are formulated and are solved with the commonly-used Runge-Kutta method. It is shown that the vibration amplitude of stay cables increases with the increasing Coulomb damping force. It is thus concluded that the cable surface materials have an important effect on cable vibration and the use of surface materials with good hydrophobic performance reduces the vibration amplitude of stay cables.