This work investigated a coupled computational fluid dynamics and population balance modeling (CFD-PBM) approach to predict the hydrodynamic behavior of the complex gas-solid two-phase flow in a three-dimensional (3-D) polydisperse propylene polymerization fluidized bed reactors (FBRs). Four different drag models, namely Syamlal-O'Brien, Gidaspow, McKeen and EMMS, were incorporated into the CFD-PBM model for evaluating the different effect of drag force between the gas and solid phases. Simulation results revealed a significant effect of the drag model on gas-solid flow in polydisperse polymerization FBRs. It was found that (1) compared to Syamlal-O'Brien and Gidaspow drag models, McKeen and EMMS drag models could predict a lower bed height, a higher temperature and an obvious core-annulus structure in polymerization FBRs; (2) EMMS drag model outperforms the other three drag models with respect to pressure drop prediction; and (3) the drag coefficient had little influence on the evolution of Sauter number and particle-size distribution. (C) 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.