Experimental results of dynamic features of traveling wave of vortex-induced vibration(VIV) of a long slender cylindrical structure were given. The experiments were carried out in a water tank. In order to observe the occurrence of travelling wave in the tank of limited width, the aluminum pipe of 0.006 m in diameter and 3.31 m in length was used, so the aspect ratio of model is over 500. The structure was dragged by a trailer whose velocity can reach 1.5m/s. The weight of 2.5kg was employed to provide the end tension. A method that was used to assess the contribution of traveling in whole vibration waves was introduced. The traveling wave ellipse was employed to fit the distribution of the amplitudes of vortexinduced vibrations along the length of the model. The experimental results show that, the traveling wave appeared over a given velocity range and when the velocity was 0.9m/s, the traveling wave was notable. Except the velocity is 0.9m/s, the traveling wave ratio is around 0.2. Result showed the travelling wave under low mode was observed, this is beyond the limit defined by travelling wave criterion. Finally based on observation of experimental data and theoretical analysis, a new traveling wave formation phenomenon was given.