Dynamic response of conductor breakage is analyzed on guyed oxytropis transmission tower-line system of 500KV 5291 JinJiang-Zhenjiang lines. Considering unbalanced tension, finite element method is presented. Result of the transient analysis shows that the vibration of tower-line system happens after conductor breakage. With the damping affect，the system vibration becomes gentle. For the tension of lines, the peak value of dynamic tension of conductor can be times of the initial tension. It is shown that the proposed method is of efficiency and practicality.