This paper focuses on the estimation of the maximum impact force of dry granular flow upon a rock shed using a coupled discrete element method (DEM) and finite element method (FEM). The dry granular flow is modeled as an assembly of discrete particles, and the rock shed is modeled by applying the FEM. The coupled DEM–FEM approach calibrated with a small-scale physical experiment is used to simulate the movement of a dry granular flow impacting the rock shed. Full-scale numerical modeling based on the field model is constructed to estimate the maximum impact force of dry granular flow on a rock shed. Based on the numerical results, three key stages of the impact process are identified: startup streams slippery, impact, and pile-up. The sensitivities of bulk density, impact height, slope angle, cushion thickness, and friction coefficient to the maximum impact force are 1, 0.63, 2.68, 0.09, and 0.73, respectively, in the benchmark model, and the parameters with high sensitivities should be given priority in the design of rock sheds. Moreover, an evaluation formula of maximum impact force is obtained and based on the numerical results and Buckingham’s principle.