Seismic responses of power transmission tower-line system under multi-component excitations were analyzed by numerical simulation. A three-dimensional finite element model of transmission tower-line coupled system considering the geometric nonlinearity of transmission line was established. Twelve seismic records of different soil types were selected based on Code for Design of Seismic of Electrical Installations. Seismic responses of power transmission tower-line system under single component, two horizontal component and multi-component excitations were investigated using nonlinear time history analysis method, respectively. The results show that the responses of transmission tower-line system under multi-component excitations are significantly larger than those under single component excitation only, especially for considering vertical ground motion excitation only, and neglecting multiple nature of ground motion in analysis will underestimate the responses of the structure. To obtain an accurate seismic response and a better seismic design of transmission tower-line system, multi-component ground motion inputs need to be considered. The results provide reference for seismic design of transmission line practical engineering.