Digging is one of an important part of afforestation. To promote mechanized afforestation in hilly regions, this paper study the work process and the principle of the auger during the drilling under the ground based on the discrete element method (DEM). The effect of spiral blade geometry on soil disturbance and soil-soil soil-tool interaction forces in a cohesive soil was assessed in a virtual soil bin using the DEM. Combined with the mechanical analysis and simulation results, the soil throw trends, the energy change, the influence of parameters is analyzed on the spiral blades. The main influencing factors for soil uplift are the drilling speed, the helix angle of spiral blade, the soil characteristics, and the feed velocity. Based on that, this study also explores the formation conditions and mechanism of the fish-scale pits on the slope to the soil and water conservation. To test the result, a verification experiment has been carried out in arid and semi-arid hilly forest areas. This research provides a theoretical reference for the innovative research, development, and design optimization of the earth auger in hilly regions.