Most　of　previous　studies　on　wind-rain-induced　cable　vibration　were　carried　out　in　a　wind　tunnel.　These　wind　tunnel　or　wind-rain　tunnel　tests　do　reveal　some　important　features　of　wind-rain-induced　vibration　of　prototype　stay　cables　observed　from　site　measurements.　However,　there　are　some　differences　between　a　rigid　inclined　cylinder　and　a　prototype　stay　cable.　This　paper　is　aimed　at　exploring　the　mechanism　of　the　wind-rain-induced　vibration　of　the　prototype　stay　cable.　Extensive　parametric　studies　are　performed　to　investigate　the　effects　of　main　parameters　on　the　wind-rain-induced　cable　vibration.　It　is　shown　that　the　occurrence　of　the　wind-rain-induced　cable　vibration　is　mainly　because　of　the　alternating　aerodynamic　damping　ratio　and/or　the　alternating　excitation　force　due　to　the　interaction　between　rivulet　motion,　cable　motion　and　wind.　The　increase　of　the　cable　structural　damping　can　effectively　suppress　the　wind-rain-induced　vibration　of　the　cable.　The　static　tension　force　in　the　cable　influences　the　vibration　response　of　the　system　moderately.　The　power　exponent　in　the　wind　profile　has　some　extent　effects　on　the　vibration　response　of　the　system,　in　particular　on　the　critical　mean　wind　speed.