Abstract: Upon the random packing of mono-sized spherical particles in a cubic container,DEM was applied to simulate the re-location of particles in gravity field.Movement of the packing particle could also be traced during the simulation.Computed results showed that under the gravitation the packing tended to be more uniform and denser with both the ultimate density and the average coordination number increasing obviously.It was found that relative dimension of the boundary,ratio of particles radium to length of cubic container,had a significant influence on the parameters of packing density and coordination number.