In the context of power application in a wide range, it is of great significance to study the vibration characteristics of transmission lines for the overall security of the power grid. In this paper, a simplified mechanical model of three-wire two-column coupling system is derived, and a typical 500kV AC double-loop tensed-tower model is established by Ansys software. On this basis, Davenport wind speed spectrum is used to simulate the wind load of the model node of the power tower, and the validity of the analysis is illustrated. The dynamic characteristics of the tower-line coupling system are calculated by theoretical method and finite element method respectively. The results show that the theoretical calculation is consistent with the finite element results, and the validity of the theory is proved. In addition, it can be seen from the finite element analysis that some novel modes induced by tower or line appear in the coupling system, and the vibration frequency of coupling under the same order is lower than that of single tower.