Mechanical characteristics of tower and maximum jump height of conductor after ice-shedding are key issue in the design of a tower head. Ice thickness of UHV DC line in ultra-heavy ice zones may arrive at 60mm~80mm, exceeding the maximum value proposed in current transmission line design codes. The finite element models of tower-line systems of UHV DC line sections in ultra-heavy ice zones are set up, and the dynamic responses of the systems with different spans after ice shedding are numerically simulated. Stress and longitudinal unbalanced trension on the towers and the maximum conductor jump height are obtained, and the mechanical characteristics of the towers and electric isolation clearance are analyzed. It is shown that the longitudinal unbalanced tensions are larger than those determined by current deighn code and the maximum conductor jump heights are larger than those by current formulus. The longitudinal unbalanced tension on the towers and the modification to the jump height formula are suggested.