Yaw damper would manifest complex dynamic performance when vehicles run. Different dynamic performance would happen between new yaw damper and old yaw damper. Different installation length would show various dynamic feature. The analysis on new damper and old damper and various installation length were discussed. It could be concluded that dynamic stiffness and dynamic damping were both reducing when damper served for a long time, which was more obvious when amplitude was small, and the difference between new damper and old damper would become smaller with the increasing of amplitude; The dynamic stiffness and dynamic damping would reduce with the increasing installation length; Dynamic damping would reduce with the augment of installation length with small amplitude or big amplitude and low frequency; There was no obvious changes between dynamic damping when amplitude and frequency were big enough.