In consideration of the attenuation effect of damping, the ice-shedding loadings of transmission lines was regarded as a kind of sudden dynamic loadings on the basis of the principle of function and law of conservation of energy, and the formula for transmission lines jump height was deduced. The dynamics essence of jump induced by the ice-shedding was revealed in the formula, a quantitative relation between the jump height and the amplitude difference was built. The example analysis shows that the results between the formula and the finite element correspond well, which meets the engineering design requirements and provides theoretical guidance for transmission lines design.