Abstract: This article deals with the processes and mechanisms of channel adjustments of the main stream and a tributary, the Yangchangzi River, upstream of Hongshan reservoir on the Laoha River, which is located in the northeast of China. The channel adjustments are reflected by changes of channel capacity, ratio of square root of channel width to depth, slope, bed material composition and channel pattern. It was illustrated that, in the processes of channel accretion headward caused by uplifted water level, the feedback couples between main stream and tributaries, between upper and lower reaches, between channel and floodplain and between ecosystem and river system were getting active. Under the influences of the complex feedback mechanisms, the channel capacity of the studied reach had undulated obviously in the general decrease tendency, the channel slope and the median grainsize of bed materials increased after strongly lowered, the geometry of channel was adjusted favorably to sediment transport in long term. The channel pattern of the studied reach has changed from wandering to sinuous under the influences of many factors. The adjustment of the channel of the tributary showed similar characteristics as that of the main channel. The sediment concentration of the tributary decreased after its erosion basis was raised.