In this study, a series of inclined model experiments were conducted to investigate the behaviour of reinforced soil walls with leakage of backfill material. The experimental results were simulated by discrete element method (DEM). From the results of the inclined model experiments, it was confirmed that the tensile force in the reinforcement near the wall facing decreased due to the leakage of the backfill material, while decreasing the horizontal resistance of the reinforced soil wall remarkably. The leakage behaviour observed in the experiment was simulated using DEM. From the results of the DEM simulation, the calculated displacement pattern was found to be roughly similar to that obtained in the experiment. During leakage of the backfill material, an area without normal contact forces was generated at the lower end and this area developed toward the upper side. Such a change in normal contact forces affects the behaviour of a geogrid, in particular the disappearance of normal contact forces weakens the interlocking between the geogrid and the soil. This observation agrees with the experimental finding that the strain of the geogrid decreased in the area near the back of the wall facing.