Abstract: The radioactive graphite dust generates during the operation of high temperature gas-cooled reactor, which exerts certain impacts on operational and environmental safety. In this paper, the two-dimensional pebble bed flow field was selected, and the influence of pebble bed structure on the diffusion and deposition of graphite dust particles in the reactor core was analyzed by using the discrete phase model. The calculation results show that the pebble bed structure could effectively prevent the spread of the graphite dust particles. The number of deposited dust particles on the pebble bed increases with the helium flow rate, while the trend of the growth is limited due to the inertia of particles and the effect of thermophoresis force. The deposition efficiency of graphite dust particles presents a trend of almost unchanged-rapid growth-slow growth associated with particle size in the flow field of the pebble bed structure.