Abstract: In this paper, the adjustment of the lower channel of the yellow River and the response to the variation of the base level resulted from clear-water scouring have primarily been studied during the operation of Sanmenxia Reservoir from Septmber 1960 to October 1964.In the variable condition of the discharge and the sediment fed into the channel, the adjustment of the longitudinal profile has been explained mainly in two ways.First, the variation of the gradient in the whole lower channel and each reaches have been analyzed.The gradients from Tiexie to Lijing, Tiexie to Gaocun and Gaocun to Lijing in I960 and 1964 are 1.52‰ and 1.5‰ 2.14‰, and 2.12‰ and 1.13‰ and 1.13‰, respectively.Secondly, the scoured depths have separately been calculated in the upper and lower reaches above and below Gaocun.It turns out that the accumulated average scoured depth is 1.51M in the whole lower channel from 1960 to 1964, and 1.52 M and 1.49M from Tiexie to Gaocun and from Caocun to Lijing respectively.It shows that the scoured depth along the channel is nearly a constant, that is, the lower Yellow River adjusted its longitudinal prifile in the approximately parallel deepening processes of the stage of clearwater scouring.The stabilities of the channel of the upper and lower reaches above and below Gaocun are slightly diffrent.This diffrence can be illustrated by Lokhtin's number of the upper and lower reaches.The Lokhtin's number of the upper reaches is small, which means that it has a big gradient.The result is that the bed material size doesn't fit the gradient of the channel.The greater gradient in the reaches is primarily relative to the deposition in the past geological process, This is why the braided channel has a greater gradient.The lower reaches below Gaocun have a greater Lokhtin number first because of the sinuosity of the channel.Secondly, the gradient becomes smaller and the bed material size is finer under the influence of the downstream extension of the river mouth.The adjustment of the cross section of the channel, particularly in the upper reaches at railroad-bridge makes the channel deeper and narrower.The change of channel patterns depends mostly upon the geomorphic threshold and the content of silt-clay in the channel material.It is rather possible that the braided channel pattern from Tiexie to Gaocun will develop into a single braided pattern because scouring causes the slope of the channel close to or less than the geomorphic threshold and also causes the roughering of the channel bed material.The principal reason of nonequilibriun of the lower channel of the Yellow River in the Long time-span is the influence of the geological and geomor-phological process and the base level.Even if some area could be under control in the future by providing with rough sediments and good consevervation of water and soil, natural erosion will be continued and is tremendously difficult to be controled because of the geological proccess in the long-time duration.Thus, the sediment fed into the Bohai sea can't be greatly reduced and the river mouth will be continuously extended toward the sea.In fact, the distributary mouth of shenxiangou was extended toward the sea by 6.25 km.during 1961-1964, about 2.08km per year, the velocity of extension was faster than that before the construction of Sanmenxia Reservoir.This proves that the effects of the base level on the upper channel still exist.From long term view, basically the aggradation behaviour of the lower channel would not change.