The project of 500 kV four-circuit on one large crossing transmission tower in Xijiang was introduced. This paper analyzed and compared the dynamic characteristics of single tower and tower-line system. Both in the single tower and tower-line system, the first modal is x-axis bending vibration, the second modal is y-axis bending vibration, and the third modal is z-axis torsional vibration. The y-axis bending vibration frequency and z-axis torsional vibration frequency of the single tower are smaller than those of the tower-line system. The results show that the structural system layout of large crossing transmission tower is reasonable and the wire can improve the bending stiffness of y-axis and the torsional stiffness of z-axis.