The particle motions in a fluidized bed were numerically simulated using a Eulerian-Lagrangian model. The solid phase was modelled via the Discrete Element Method (DEM) while the hydrodynamic model of the fluid phase was based on the volume-averaged Navier-Stokes equations. A fluid density-based buoyancy (FDB) model was adopted to calculate the solid-fluid interaction force. In this paper, the complex ‘four way coupled’ interaction as proposed by Elghobashi in 1991 was modelled, namely the dominant effect of gas phase on the dispersed particles, the back influence of the particle phase on the gas phase, and interactions between particles such as collision, agglomeration and break-up. A stable succession of bubble formation and disappearance was captured. Obtained pressure drop and interparticle contact number had a good agreement with those reported in previous reference