Abstract: By using laboratory model tests, the unconstrained sliding and accumulation of gravel on an inclined board are studied. The influences of various parameters of volume, gravel size, shape of accumulation, height of slope, angle of initiation region, constraint angle of slope toe and friction coefficient of sliding surface on the characteristics of final accumulation (run-out, width, thickness, and area) are investigated. The results show that with the increase of volume of accumulation, grain size, height of slope, angle of initiation region and constrained angle of slope toe and the decrease of friction coefficient of sliding surface, the scope of the final accumulation is expanded. The lateral extension motion of gravel on the slope has two different mechanisms: sliding to the slope toe with a certain angle, and sliding downward along the direction perpendicular to the slope toe when the lateral extension reaches a certain width. It is confirmed that the volume of accumulation, friction coefficient of sliding surface, gravel shape and constrained angle of slope toe are the most significant factors to influence the run-out and accumulation area, and the height of slope and volume of accumulation have significant influences on the width. Finally, the test results may provide a preliminary basis for further studies on landslide run-out and accumulation characteristics.