Abstract: Three-dimension model for rain-wind-induced vibration of stay cable is established, in which the lag of stay cable is considered. Based on the assumption that the motion of rivulet is harmonic and tts frequency is equal to the first modal frequency of stay cable, the in-plane and out-of-plane displacement response at the 1/2 length and 3/4 length from the top of stay cable, and their amplitude-frequency curves are obtained. The results show that the vibration of stay cable is mainly single-mode vibration. In-plane vibration is the chief danger to the safety of stay cable. Two MR dampers are applied for vibration mitigation. The relations among modal damping ratio and voltages and the location of the dampers are investigated. A segment of displacement response when it achieves stationarity is obtained. It’s shown that the modal damping ratio has an optimization voltage, and the effect of vibration mitigation will be better when the location of dampers is a bit higher.