A high accuracy experimental system has been established for unsteady open-channel flow.Then 40 experiments were conducted to study the propagating characteristics of unsteady open-channel flow.From the experimental data,the variation law of propagating velocity,wave deformation rate,flow depth of wave peak and bottom,and other parameters were obtained.The experimental results show the followings.1) The propagating velocity of unsteady open-channel flows can be expressed by the sum of flow velocity and micro-amplitude wave velocity at wave peak.2) The waveform of an unsteady flow would deform when it propagates,with the rising stage becoming longer and the falling stage shorter;the deformation rate is a function of distance,period and relative amplitude of discharge.3) The flow depths of wave peak and bottom have a close relationship with the period of the unsteady flow.When the period is short,water depths of wave peak and bottom are both close to those of the average discharge in the condition of uniform flow.For a long period unsteady flow,the water depth of wave peak is close to that of the maximal discharge in the condition of uniform flow,while at the flow wave bottom,it is close to the depth of the minimum discharge in an uniform flow.4) Propagating characteristic of discharge is analogous to that of flow depth for unsteady flow. A high accuracy experimental system has been established for unsteady open-channel flow. Chen 40 experiments were conducted to study the propagating characteristics of unsteady open-channel flow. From the experimental data, the variation law of propagating velocity, wave deformation rate, flow depth of wave peak and bottom, and other parameters were obtained. The experimental results show the followings. 1) The propagating velocity of unsteady open-channel flows can be expressed by the sum of flow velocity and micro-amplitude wave velocity at wave peak. 2 ) The waveform of an unsteady flow would deform when it propagates with the rising stage becomes longer and the falling stage shorter; the deformation rate is a function of distance, period and relative amplitude of discharge.3) The flow depths of wave peak and bottom have a close relationship with the period of the unsteady flow. WHen the period is short, water depths of wave peak and bottom are both close to those of the average discharge in the For a long period unsteady flow, the water depth of wave peak is close to that of the maximal discharge in the condition of uniform flow, while at the flow wave bottom, it is close to the depth of the minimum discharge in an uniform flow.4) Propagating characteristic of discharge is analogous to that of flow depth for unsteady flow.