Abstract: A study is carried out on an iced transmission line under the axial excitation caused by the vibration of an adjacent span, in which geometric nonlinearity and aerodynamic nonlinearity are considered. On the basis of a Hamilton principle, a two degree-of-freedom dynamic model along with boundary conditions are established for describing the coupling of in-plane and axial vibrations. The reduced model is derived by eliminating the axial vibration and Galerkin method is then applied to spatially disperse the partial differential equation. The basic range of the excited force is determined through the calculation of dynamic tension initiated by the adjacent span. Numerical procedures are implemented to analyze the influences of excited frequency and force on the system. Abundant motion patterns of period-doubling, almost period and chaos, are observed when the excited frequency is approximately equal to the natural frequency of the iced transmission line. The numerical verification is carried out on the single-span to further prove that galloping of an adjacent span can lead to an obvious increase of amplitude, a decline of critical wind velocity, the invalidation of increasing damping, and the instability of iced transmission line galloping, providing a theoretical support to practical engineering.