Insulation clearance should be taken into account in the tower design of transmission lines in an ice zone, which is closely related to the jump height of conductor lines after ice shedding. Because the existing formulas for jump height of conductor lines after ice shedding are inapplicable to the lines with large span length and evelation difference, this research focuses on the finite-element simulation of dynamic responses of transmission lines with large span length and elevation difference after ice shedding, and obtains the numerical data in relation to the jump height, its sag before and after ice-shedding, line span and evelation difference. Based on the numerical simulation results, an improved formula for jump height of transmission lines is proposed with nonlinear regression analysis, and the fomula is applicable to all the transmission lines with different span length and elevation.