Abstract: Many accident gates in water power station are controlled by tension cable-poles.The vibration of the gates generated by water turbines may induce the strong vibration of the cables,which may damage the water-gate system.Based on the experimental and theoretical analyses of the vibration damage of a watergate,the parametrically and externally excited equations of motion of an equivalent cable are established in this paper.The stability of the cable is then analyzed according to the Floquet theory.In general,the flexural resonance occurs when the frequency of horizontal motion of the gate approaches the natural frequency of the cable.However,the vertical motion of the gate will cause the instability of fundamental,super and sub-harmonic waves in cables and generate strong vibrations,which is an important cause of damage.