Abstract: Since the construction of Dan-Jiang-Kou Reservior in 1959, the reservoir regulation has markedly altered the discharge and sediment process in the channel downstream. The flood-peak hydrograph has been lowered and flattened; the period of low flow has disappeared with the discharge becoming constant at 1000-1500m³/s. Sediment load has been reduced from 1.33kg/m³ and the turbid water has become cleaner. Essential changes have taken place in the channel below the reservoir with the effect, of the reservoir regulation and regional physical conditions. Degradtion has been replaced by aggradation in the channel; the deep scour in channel thalweg by 2-4m has occurred over the whole channel; deep scour has been slowed down with the establishment of the resistant layer, and lateral erosion increased, but far it will go on depends on the boundary conditions. Degradation is dominant in the channel downstream from the reservoir and has extended up to the mouth 630km below the dam. The channel slope has been gradually flattened except for the places near the confluences of major tributaries where the channel slope becomes steeper due to the aggradation caused by these tributaries of heavy sediment load. The relationships between channel geometry and discharge and sediment load have been improved with a relative factor up to more than 0.8 compared with what they iwere. Since the increase of channel depth is more rapid than that of the width while there is no increase in velocity as the depth increases, the channel geometry has been subject to much alteration; the flow has concentrated into the channel; deep scour of the channel has occurred and sinuosity of the channel thalweg has increased. Consequently, the height difference between the bed and surface of bars has increased;branch channels have been filled up and the channel pattern has changed-from multichannel to the single channel, with the width depth ratio being reduced to about 10. Small bars have joined to become big bars and lower bars have been transformed to higher ones which have after then become terraces. Bank slumping has slowed down as a result of stabilization of bank slope and coarsening of bank material.According to the distance away from the dam and regional natural conditions, the channel downstream from the reservior can be divided into three parts of different characteristics, 1, near reservoir reach (Dan-Jiang-Kou-Nou-Shou) which is more than 90Km long and most markedly affected by reservoir regulation and channel adjustment is rapid so that the straight wandering channel has been transformed to the single restricted meander with sinuosity being increased from 1.25 to 1.50; 2, the reach influenced by Tang-Bei-He river; Its length is 70km. In this reach the channl remains wandering as a large amount of coarser material coming from major tributaries has disturbed the channel self-adjustment. 3,the lower reach which has a length of 460km and less affected by the reservoir regulation owing to the long distance from the dam. In this reach lateral migration has become wea kened in the wandering channels whereas the deep erosion has developed and sinuosity has increased in the meandering channels with the effect of bank material.