[Purposes] The paper aims to study the influence of the coupling between transmission line and tower on the wind-induced dynamic response of the tower-line system. [Methods] Combined with the example of a tower-line system (three towers and two lines), numerical calculation and wind tunnel tests of an aeroelastic model were conducted. A finite element model of the above tower-line system was established with ABAQUS software, and the wind load generated by the harmonic synthesis method was used as input along the downwind direction. The Newmark-β method was used to solve the dynamic response of the system in the downwind direction. The wind-induced vibration coefficient of the system was calculated and compared with various codes. [Findings] The numerical analysis results are in good agreement with the experimental results, and the wind-induced vibration coefficients are all higher than the recommended values in the code. [Conclusions] The existence of transmission lines improves the aerodynamic damping of the structure, resulting in the acceleration response of the tower-line system being lower than that of a single tower. The wind-induced vibration coefficient increases with height, with a local mutation on account of the local mass increase of the cross arm. In practice, when calculating the wind-induced vibration coefficient of the transmission tower structure, the influence of transmission lines on the cross arm should not be ignored, and the suggested values of various codes should be considered comprehensively.