Abstract: The 10 MW High Temperature Gas-cooled Reactor (HTR-10), developed at Tsinghua University, is an important test advanced reactor in the world. The pebble flow is of fundamental significance for the HTR-10. The discrete element method validated by experiments was used to study pebble flow in the HTR-10 core by the phenomenological method. A 1∶1 scale computational model to the HTR-10 was utilized to simulate the motion of 27 000 spheres, including the flows with different frictional coefficients and base angles. It is found that the pebble flow inside the HTR-10 core is uniform. The stagnant region does not exist. The larger the frictional coefficient or the base angle is, the more uniform the pebble flow is. When the frictional coefficient is 0.8, the HTR-10 maintains a normal discharge operation without stagnant pebbles. This work is important to further optimization of HTR design and development.