Abstract: Rapid landslides are very dangerous mass movements in mountainous regions. The accurate prediction of the run-out process of these landslides is crucial for risk management and prevention of potential disasters produced by them. As a very promising method for the run-out prediction of rapid landslides,the material point method(MPM)has been widely applied in simulating the run-out process of rapid landslides along two-dimensional longitudinal slope profiles,but it is difficult to account for complex three-dimensional(3D)topography in this method. Therefore,in this paper we propose an improved 3D MPM model which is capable of modeling rapid landslides propagating on complex topography. In the new MPM model,an algorithm was formulated for calculating the unit normal vector of the sliding bed,and normal momentum constraints were imposed on the background grid nodes to reflect the influence of curved sliding bed on the sliding mass. The proposed MPM model was validated by simulating a granular flow test conducted in a curved flume and the Yanjiagou landslide that occurred in Shanyang County,Shaanxi Province,China. The simulation results of the granular flow test indicate that the maximum velocity at the flow front can reach 1.1 m·s^-1,and the simulated positions of the flow front and tail agree well with the experimental results. The simulation results of the Yanjiagou landslide show that the main body of the landslide propagates on the sliding bed dipping out of the pre-failure slope,while a small amount of sliding mass at the rear part of the landslide separates from the main sliding mass and transports along the gully channel on another side of the mountain ridge. The deposition zone of the landslide is mainly divided into two parts by the mountain ridge. The maximum velocity of the landslide is greater than 20 m·s^-1,and the maximum thickness of the deposit appears in the gully channel at the slope toe,which is approximately 49 m. These simulation results are consistent with field observations. Additionally,the moving direction of the landslide changes twice along the twisted gully,and the landslide climbs up the gully slopes in this process. Our model overcomes the sliding bed penetration problem of the traditional multi-material contact algorithm and saves computational costs for dealing with complex sliding bed boundary conditions. The model can efficiently simulate these run-out characteristics of rapid landslides over complex topography,and the simulation results may provide useful references for guiding the mitigation and prevention of such landslides.