As the "internal source" of pollutants in water, polluted sediment has become a serious hidden danger of water environment for the water that exogenous pollution has been controlled. As a technique to prevent the secondary contamination of sediment, in-situ covering technology is limited in its development due to its disturbance to sediments during the covering process. To solve this problem, a new method using patchy soil as in-situ covering material has been proposed, and the law of material settling in water has been studied. The settlement experiment was carried out by using the silt as the material, and the relationship between the settling velocity of the material, its tangential Angle and its own properties was mainly concerned. The results show that the tangential Angle of the material does not affect the settling velocity of the stable settlement. When the material settlement is stable, the speed is proportional to the thickness and density of the material.