Abstract: Discrete element method was used to simulate the pebble dynamics in the high-temperature gas-cooled reactor core, based on the two-dimensional pebble dynamics experiments. Phenomenological method was used to analyze the formation of the two-region distribution, the central, mixing and stagnant regions, and the velocity distribution. The simulation results show that a stable central region is formed, mixing zones between the central and annular regions and stagnant regions are observed in current simulation. The closer to the bottom of the pebble bed, the more uneven the vertical pebble velocity and the bigger the horizontal diffusion.