A combined Computational Fluid Dynamics and Population Balance Model (CFD-PBM) was developed to study the flow hydrodynamics of the slurry bed. The CFD-PBM applied a modified drag force model by considering the reduced drag force between gas and liquid phases at the presence of particle. Results show that the CFD-PBM with the modified drag force model can reasonably predict the flow hydrodynamics compared with the experimental data. It was predicted that the increased particle loading can enhance bubble coalescence to form larger bubbles, which can flow faster and reduce the gas holdup in the slurry bed. In addition, simulation results indicate that the particle flow becomes more non-uniform with much faster upward flow in the center and downward flow near the wall with the increase of superficial velocity. Particle back-mixing can be enhanced at higher superficial gas velocity, which can be beneficial for the reaction system with limited decrease in catalyst particle's reaction activity and unbeneficial for the reaction system with almost fully deactivation of catalyst. (C) 2019 Elsevier B.V. All rights reserved.