Abstract: Rain-wind induced vibration (RWIV) is the phenomenon that a stay cable may vibrate with a large amplitude and a low frequency under the special conditions of wind and rain. According to lubrication theory and vibration theory of a single-mode system, the coupled equations of water film evolution and cable vibration are presented. The wind pressure and friction coefficients in water film evolution equations are obtained by computational fluid dynamics (CFD) software-Fluent. To reveal the mechanism of RWIV, the relationships between the water film morphology, the lift and vibration of a cable are discussed by numerical solving the coupled equations. The results show that cable lift oscillates periodically due to the periodical variation of water film morphology, which causes the large amplitude vibration of a cable. This confirms the conclusion that the main reason for RWIV is the resonance between rivulets and a cable.