Abstract: In order to better understand the flow features of binary mixtures in pebble bed which is composed of pebble clusters and pebbles, discharging characteristics of the binary mixture material of pebble cluster and pebbles were simulated by DEM. The pebble cluster was composed of three particles connected by rigid bonds, forming angles of 60°, 90°, 120° and 180° and being discharged from the discharging hole at the bottom of pebble bed with different number fractions. The discharging characteristics of pebble clusters and pebbles of different number fractions and included angles were quantified. The results show that the existence of pebble clusters can reduce the discharging rate, and the degree of reduction is negatively correlated with the increase of the included angles and the number fraction of pebble clusters. When the included angle and the number fraction of pebble clusters increase, the discharging rate reduces.