The regulation of Three Gorges Reservoir(TGR) and reservoir deposition have changed the characteristics of coming water and coming sediment of middle-lower Yangtze River, the sediment-laden entrancing the downstream of the Three Gorges Dam(TGD) has been greatly decreased, so clear water discharged over the spillway of the dam is scouring the river-beds and river banks and then sediment-laden volumes along distance are being gradually recovered. On the basis of previous studies, a 1-D mathematics model simulating TGR sedimentation and scouring-silting of the dam downstream was established with the conditions of TGR early 20-year operation and adding a new water-sediment series-year. Annual coming water volume, annual sediment transport amount and their changing trends along distance at several hydrologic stations were analysed. The calculated results were compared with measured data, and corresponding values were basically close. So the results of this research are rational, believable.