Understanding the behavior and quantifying the impact force of a granular sliding mass are crucial to landslide hazard assessment and designing protective structures against landslide debris. The study of a granular sliding mass provides useful insight into the characteristics of sudden onset, rapid granular flow. There are several factors, such as inclination angle, basal friction between the granular flow and the flow bed, particle size and shape, and distance to a rigid obstruction, which influence the impact force and behavior of granular flow. In order to systematically investigate the effects of these factors on the impact force from granular flow, a two-dimensional sand flume was designed and constructed. This sand flume included a load measurement device consisting of six dynamic load cells, which served as the rigid obstruction. In this study, the effects of particle characteristics on the impact force were studied by using two different granular materials with mean particle sizes of 0.25 and 1.98 mm. Impact forces and flow front velocities were measured and compared. The results indicate that the different basal friction angles for the two materials result in different flow velocities and final static forces. Moreover, the different flow velocities, densities, depths, and stiffness result in different dynamic force components.