Abstract: In this article the experiments of open channel flume is done to study the coherent sediment motion in weak dynamic condition, the experimental results indicate that the special movement form "the lamination movement" emerges when the condition (flow and sediment density) is contented.When "the the lamination movement" occurrs, the sediment density along perpendicular profile presents "the steps and ladders".The peak value of the fluent speed emerges in the middle of the perpendicular of the flow, then reduces to the water surface and the bottom of the flume.The cohesive sediment flocculation and construction of flocculation net are the basic reason for the emergence of the lamination movement forms.The fluent condition is the most important factor for the lamination movement formation, and the lamination movement forms in the certain fluent intensity scope.The sediment density has the tremendous effect on the lamination movement formation.Different sediment densities form the different lamination movements and the hydrodynamic conditions, that is the silt density increases, the intensity of the fluent forming the lamination movement also increase correspondingly.