The adhesion of soil is a very important technical indicator in the dredging engineering, which can provide reasonable suggestions for the selection and operation technique of digging machine and offer design and construction parameters for the excavating and jetting-filling projects of channel, harbor basin, but the research of adhesion is still at a preliminary stage now. Seven typical soils in dredging engineering were chosen to do physical property and cohesion tests, connecting the physical indexes and cohesion of soil at soil mechanics level and discussing the adhesion mechanism of soil at soil properties level. The results showed that, the higher the clay content of soil, the larger the adhesion. The adhesion increased gradually with the increasing of moisture content and reach peak when the moisture content was closed to liquid limit and then decreased gradually. The generation and variation mechanism of adhesion were mainly due to the change of properties and content of bound water, which caused the generation, development, equilibrium and damage of adhesion and dissociation force in water-soil-electrolyte system. The results also showed that, the adhesion of soil in natural moisture content was about 5 times the plasticity index numerically. In dredging engineering, the area with large thickness muck should be excavated with water filling and for soil containing more gravel, sand and silt drainage measure should be enhanced to increase the digging and spoil disposal speed.