Objective： To clarify the interaction mechanism model between screw and grain in grain pile depth, and to determine the mechanical characteristics of screw of spiral robot for granary at different speeds and depths, so as to provide the design basis for the motion control system. Methods： Using mathematical model, combining Janssen grain storage pressure theory and Janosi shear-displacement equation, the shear stress model was established, and then the thrust model of screw was derived from the shear stress model. Through the design and construction of the experimental device, the combination of different speed and pressure was used to carry out the all-factor experiment, and the measured experimental data was compared with the theoretical value. Results： The theoretical value of the thrust model was close to the experimental value, and the curve variation trend was the same. The average relative error of the axial thrust model was 14%, and the average relative error of the resistance torque model was 24%. Conclusion： The screw thrust model based on Janssen grain storage pressure theory and Janosi shear-displacement equation at different depths has high reliability.