Dynamic characteristics and seismic response of long crossing transmission single tower and tower-line system were systematically studied by time-history analysis method. The different dynamic characteristics between the long crossing transmission single tower and tower-line system have been found and come up with some feasible suggestions. With practical engineering background, the seismic response differences of the displacement, torsion and axial force in main leg and web member of the single tower and tower-line system are studied. The results show that: Compared with the single tower, the main mode shapes of the tower-line system are almost equal, however, the fundamental period of the towerline system which takes the combined activate into consideration prolonged evidently. Meanwhile, it's also coupling vibration of line. In addition, the maximum nodes displacement of the single tower and tower-line system are relative to the nodes location. The torsion of tower-line system becomes much gentler than the single tower with the seismic travel time increases. Because of transmission line, the axial force of the tower-line system of the bottom of tower leg and web member at the stiffness sudden change are bigger than single tower.