Analyzed the sediment-transport process in high sediment-laden river, the new concept and calculating method for sediment-transport water volume are proposed. Based on field data of sediment and water volume in the Lower Yellow River from 1950 to 2000, the sediment-transport water volume and unit sediment-transport water volume in LYR are calculated. Meanwhile, relations between them and influencing factors are confirmed to calculate efficient sediment-transport water volume after construction of the Xiaolangdi reservoir.