After impoundment of the Three Gorges reservoir，the incoming water and sediment conditions of its downstream river reach are changed.Consequently,changes occur in the riverbed evolution.On the basis of measurements and research findings by predecessors,aiming at the downstream reach of bed sediment composition,in order to study the riverbed evolution,we carry out physical model test by the double sand method to study the variation of river regime of the reach,which provides reference for the the next stage work.