Abstract: The flume experiments on the mobile sand bed are made in this paper.The frequent group initiation of bed material is found to occur by the turbulent sweep.The sand-wave movement is also observed.According,two physical models of the bed material exchange in different levels are presented to prove the coarsening of surface bed material makes the recovering distance much longer than that for the condition of uniform bed material,and thus greatly effects the non-equilibrium sediment transport process.The new boundary condition considering the coarsening of the surface non-uniform bed material is obtained.Lots of non-equilibrium sediment transport process in different hydraulic and bed material conditions are calculated by the new lognitudinal-vertical 2-D mathematical model of non-equilibrium sediment transport considering the coarsening of surface bed materiel.Finally,the experiential expression of the recovering coefficient of sediment concentration is discussed.