Abstract: Targeting sediment mixtures of different grading compositions, a series of settling experiments were conducted to systematically investigate the influence of grading on the constrained settling characteristics of sediment mixtures. The study analyzed mass concentration distribution, the settling velocity of the clear-muddy interface, and the thickness of the sediment layer. Results indicate that the constrained settling phenomenon of sediment separation is particularly pronounced when the silt mass fraction is between 35% and 38%, which can be considered the critical value for the transition in constrained settling modes of sediments with different grading compositions. The settling velocity of the clear-muddy interface increases linearly with the silt mass fraction or median particle size. An empirical formula for the silt mass fraction and interface settling velocity was derived based on experimental data under conditions of a suspended sediment mass concentration of 100 g/L and a salinity of 3‰. The sediment layer thickness decreases gradually with an increase in silt mass fraction. When the silt mass fraction is low, clay-dominated settling leads to the accumulation of large flocs, resulting in a thicker sediment layer. As the silt mass fraction increases, flocculation weakens, and silt-dominated settling occurs. The structural concentration approximates that of a silt content of 69%, leading to a thinner sediment layer.