Although the filtration efficiency can be increased because of the use of small-sized particles in granular beds, the bed pressure drop may be increased. This study presents a numerical solution of a moving bed that can facilitate instantaneous separation of binary particles into a top layer of larger particles and a bottom layer of smaller particles during the flow. The particle discrete element method is used to simulate the flow process of binary particles, which is verified by experiments. An index to measure the effect of stratification and the separation degree (SD) are proposed. Results show that SD increases as the particle size ratio and the mass fraction of coarse particles increases. The thickness of the coarse particle layer increases as the mass fraction increases. The surface thickness and segregation are within the optimum when the particle size ratio is 2.5 and the mass fraction of coarse particles is 65%. (C) 2020 Elsevier B.V. All rights reserved.