In order to study the relation between the settling velocity of sediment and the change of sediment bulk density in Danjiangkou Reservoir, and adopting the various sediment particle sizes taken on from different reservoir segments, the sediment settlement experiments were carried out under the conditions of different pipe diameters, different water depths, and sands adding respectively. During the experiments we found many especial phenomena. By comparing and analyzing the experimental data and the measured data, the results show that the velocity of sediment deposition is independent of the surface layer water depth, but the sediment bulk density changes with the velocity of sediment deposition.