Abstract: The presence of organic matter in soil has a significant effect on the soil-metal interface adhesion, but its influencing law and mechanism have not been systematically studied. By adding peat to montmorillonite, illite and kaolin, three groups of clay samples with different mineral and organic matter contents are prepared. The adhesion between the soil-metal interfaces with different moisture contents is tested by using the MC-100 tensile testing machine. The test results show that the relation curve between the adhesion force F and water content w is a typical "bell-shape" in the range from the plastic limit to the liquid limit water content. With the increase of the organic matter content w_u, the curve of F-w changes from high to flat. With the increase of the organic matter content w_u, the change of peak adhesion F_max can be divided into three stages: fluctuation or slow decline (or ascending) stage, significant decline stage, and stable stage. The saturation adsorption of the organic matter with three kinds of clay minerals is measured by the Fu's method, and the occurrence forms of the organic matter in soil change with the content of the organic matter. The mechanism analysis shows that in addition to the content of the organic matter, the form of the organic matter in soil also has a significant effect on the macroscopic adhesion of soil samples. Finally, the adhesion force of the natural peat soil-metal interface distributed along Line 5 of Kunming Metro is tested, and it is concluded that the adhesion force is small, and the risk of adhesion is also small, which is verified by the fact that the shield machine traversing through the peat layer does not show any serious adhesion to the cutter plate or clogging phenomenon.