Numerical simulation of the gas-solid flow in a three-dimensional bubbling fluidized bed is performed by means of computational fluid dynamics combined with discrete element method to investigate the solid transportation mechanism of the system. In the numerical model, gas motion is resolved in the framework of large eddy simulation, while solid phase is tracked with the discrete element method. General flow patterns of fluid phase and solid phase in both the macroscopic and microscopic views are explored to gain the insight of the interaction between bubbles and particles. Then, the time-averaged properties of solid phase are analyzed. The results indicate that a roll pair for the solid circulation can be observed. Meanwhile, vigorously lateral solid motion mainly concentrates in the regions near the bed inlet and bed surface. The vertical intensity of solid transportation is stronger than the lateral one, and the critical height of zero lateral solid flux can be used to identify the center of the roll pair. With the increase of the superficial velocity, the transportation intensity of solid phase is enhanced. (C) 2013 Elsevier B.V. All rights reserved.