Abstract: Wind load is the main control load of transmission tower, and the value of damping ratio directly affects the design value of wind load of transmission tower, the damping ratio of transmission tower is of great significance for wind resistant design of transmission lines. According to GB 5009—2012, the standard 0.01 of steel structure is generally used for the damping ratio of transmission towers. To accurately study the dynamic parameters of the transmission tower, two 110 kV transmission towers with the same structure, transmission tower and tower-line system, are tested to get the excitation response and dynamic parameters precisely. The vibration signals are obtained by using 4 different excitation methods, modified periodogram algorithm is used to denoise the response signals, half-power bandwidth method is applied to identify the dynamic parameters of response signals. The finding indicated that the ambient excitation can meet the requirements of the identification accuracy of damping ratio. Under the condition of slight vibration, whether suspend wire or not has almost no influence on the value of the damping ratio along the cross arm direction, and the value of the damping ratio of the tower-line system along the conductor direction is 20% less than that of the single tower.