Experiments were made on axial concentration distribution of binary solids mixtures in a three-phase fluidized bed of 4.2cm I.D. and 150 cm height under continuous operation mode. Biurea particles with different diameters and a mixture of biurea and blowing agent ADC with different wettability were used in the experiments.One-dimensional sedimentation-dispersion model was modified by taking into consideration of the effects of both particle size and wettability on particle settling velocity to describe the axial concentration distribution of each solids component. Agreement between experimental and model predicted data is satisfactory.