Abstract: Because to Xinjiang belongs to the arid areas, the materials of the hydraulic engineering basically are weathered soil. After evaporation the soil is dispersed due to sodium. Soil’s　dispersibility is the important element to determine whether it is suitable for the engineering and to evaluate an index of dam’s stability. By means of the experiment using the distilled water and river water, the test indicates the calcium content of the river water is higher and it can restrain the soil’s dispersion. So the water of the river has the evident affect on the clay’s dispersion.