In the present paper, a numerical study is carried out to assess the influence of bubble injection characteristics on the mixing behavior in a 2-D gas-solid fluidized bed at high pressures. CFD-DPM method is applied to investigate the particles mixing and the Lacey mixing index (LMI) is used to indicate the value of mixing in a fluidized bed. Simulation results show that constant gas flow rate as small bubbles (i.e. the small injection duration time) results in a better overall particle mixing in low pressures, but the impact of the injection duration time on the particle mixing is suppressed at high pressures due to the increased particles chaotic movements. The mixing index in x and z directions at different pressures is also investigated. The results show that the difference between the mixing times in two directions decreases by increasing the operating pressure. (C) 2016 Elsevier B.V. All rights reserved.