Abstract: Based on the double-layer theory in soil-water-electrolyte system, the relation among the dispersivity, physical, chemical and mineral properties of 48 soil samples is studied. Based on experimental researches and engineering cases, the dispersive mechanism is clarified. The results show that the influence factors of the dispersivity include clay content, clay mineral composition, organic matter, sodium ion and pH value. However, the sodium ion and pH value in the medium are the essential factors. No matter whether the clay mineral in soil is montmorillonite or illite, as long as the soil contains more sodium ions and alkaline pH, the soil will be dispersed. Both of them are indispensable.