Abstract: It is necessary to analyse the relationship between channel evolution and variation in sediment-laden floods based on the energy dissipation principle, in order to investigate the bed-forming mechanisms of an alluvial river. As an example of the braided reach in the Lower Yellow River, the characteristics of channel scouring and silting in the reach under various sediment-laden floods were presented, using a two-dimensional numerical model and the analysis of observed data. It is founded from this investigation that the relevance among bankfull area, geomorphic coefficient and characteristic values of a sediment-laden flood can reflect the restricting mechanisms in relation of the river energy; the channel scouring intensity changes periodically with various sediment-laden floods, and the accumulative scouring effect for the main channel can correlate strongly with the process of water and sediment transport; and only a flood process that can shape the most appropriate cross-sectional geometry of an alluvial river can attain both the best efficiency for sediment transport and the maximum efficiency of the main channel scouring. These results also indicate that a flood process with the maximum comprehensive factor Φ_max can obtain the best accumulative channel scouring efficiency, and therefore, the discharge corresponding to Φ_max can be considered as a control indicator for overbank floods in Lower Yellow River.