Abstract: Numerical simulation was performed on the turbulent flow of gas-solid with a binary mixture of particles in a riser.The particle motion was dealt with a hard-sphere discrete particle model (DPM).The Navier-Stokes equation was used to model gas phase flow with the large eddy simulation (LES) method.Vreman’s SGS model was used to model gas turbulence.A model of the collision time between two particles experiencing different accelerations was proposed. A binary mixture of particles with different diameters was used in the simulation and layer inversion was observed. Numerical results indicated that the flotsam of small particles had a high axial velocity and a high root-mean-square velocity, while the jetsam of large particles had a low axial velocity and a low root-mean-square velocity. At the center of the riser,triple peaks of particle velocity were found from the probability of particle velocity.However, twin peaks existed near the wall.The core-annular flow structure was observed from simulation.With the increase of superficial gas velocity,more uniform distribution of concentration and particle velocity was observed along radial and axial directions in the riser.The average particle velocity and concentration for the flotsam and the jetsam were unequal in the radial and axial directions. Numerical results were compared with the experimental and numerical results using the two-fluid model of literature. The predicted particle velocity, concentration and root-mean square velocity were in agreement with experiments at the center,but higher than the experimental values, near the wall.Gas turbulence affected the motion of small particles.The particle collisions dominated the flow behavior of particle phase in the riser.