Abstract: This paper analyzed the soil adhesion mechanism of chemical adsorption. Through study on the surface properties of soil and parts touching soil, soil water and various ion in soil water, an adhesion theory which indicates that chemical adsorption constitutes a main part was put forward. This model indicates that soil adhesion to metal surface touching soil consists of three parts, they are chemical adsorption force(including physical adsorption)between soil and metal surface, chemical adsorption force between metal and soil formed by soil water (macroscopically called capillary force) , and water viscous force.