This paper analyses channel changes of the lower reaches down reserviors and the transformations of river pattern.These rivers flow through different areas with various backgrounds and natural environments. The characteristics of channel changes under different natural conditions are.(1)The more the released discharge,the longer duration the flow and the further from the dam the erosional base level,then the longer the scour distance is;the more the discharge and the finer the material,the more intensive the scour is.(2)Three situations of channel change exist in longitudinal direction: (a)A concave or linear profile is associated with the grading of bed material and the unequality of scour over river bed (b)When bed material is composed of uniform medium or fine sand and the bed is equally scoured,the parallel lowering of the bed will occur and the longitudinal profile will inherit its original form.(c)Affeeted by the bedrock and the tributaries with heavy load, the profile will be convex.(3)Three types of transverse evolution are:(a)When both the bank and the bed are less mobile,the released discharge will primaryly cause deep scour and results in a narrowed cross-section and in decrease of width-depth ratio.(b)When the bank is less mobile than the bed,the deep scour will occur prior to the lateral erosion and the width-depth ratio might increase.(c)When both the bank and the bed are composed of uniform loose material,the deep scour and the lateral erosion will parallelly operate and less change will occur in the width-depth ratio. As far as the river pattern trasformation considered,the shorter the duration of the released flow,the more the regional storm runoff,and the worse the vegetation,then the more difficult the transformation from braided river to other river patterns.In constrast,the longer the duration of flow,the less the sediment load from the basin and the better the Vegetation,then the easier the evolution of a braided river to a single meandering river is.constrainted by the boundary conditions,these rivers may changed into a confined meandering or stable islandtype river.