The adhesion of soil to solid surface is a complicated interfacial reaction that relates to many factors. Quantitative descriptions of the forming procedures and the conditions of the adhesion interface forming can provide a guidance to the design of the soil-engaging component surfaces with a good anti-adhesion performance. Using a self-developed soil adhesion measurement device, the mean area and mean thickness of the adhesion interface waterfilm and the interfacial adhesion force varied with soil water content and vertical loads are measured. According to the gray system theory, the differential equations of the mean area and the mean thickness of waterfilm and the adhesion force of the interface are developed. The consequences between or among the factors related to the adhesion interface forming process are analyzed quantitatively with the gray correlation analyzing theory. The forming procedure of the adhesion interface and the influence on the mechanic behaviour of soil adhering on a solid surface are demonstrated by the experiments. The analysis will be beneficial to designing of soil-engaging component surfaces of terrain-machines.