Abstract: In the preparation stage of the discrete element method (DEM) simulation and the coupling of the FEM and the DEM, it is essential to generate a high-density granular assembly in a relatively short time with no overlapping in a specified region to simulate practical granular material.With a combination of geometry and physics, this paper puts forward a particle moving model for packing in 3D region.The model generates the first layer particles on the bottom of the container with the constructive method.Two different methods are adopted to calculate the moving direction of the subsequent particles according to their different contacting condition.If the particle collides with the container boundary, the direction is calculated according to the physical elastic collision theory.If the particle collides with another particle, the direction is calculated with a purely geometrical method, that is, the cross product of the particle's two consecutive contact normal vectors determines the particle's next direction, and the direction is made to have a downward trend.The model ensures that the particle contacts with different objects within three consecutive contacts, and that its final stable position converges quickly on three supporting target and satisfies the physical condition of the stationary particles.The contact detection between particles is based on the regularly partitioned grid cell in the packing area.According to the position and the moving direction of the particle, the algorithm makes full use of the characteristics of the particle moving model to search for the particles to collide in the grid cells of the grid rows at different grid levels.The experiment results show that the time to create the granular particles set is linear with the particle number and this process is completed in a comparatively short time with high-density particles set.