At present, the effect of tower-line coupling is neglected in seismic vibration control with TMD for transmission tower-line system. However, for large crossing transmission tower-line system(LCTL), the neglect can affect the performance of TMD. In this study, a typical FEM model of LCTL is established. The effect of tower-line coupling on dynamic character of LCTL is analyzed. Then, the performance of TMD considering the tower-line coupling is compared with TMD neglecting the tower-line coupling. It is concluded that tower-line coupling affect the performance of TMD significantly for LCTL.