This paper presents a numerical method coupling the discrete element method (DEM) and the computational fluid dynamics (CFD) to simulate multiphase liquid flows with poly-dispersed particles.In this coupled method, liquids are modelled using a weakly compressible flow model in the Eulerian frame with Navier-Stokes equations while the discrete particle motion is solved using DEM in which the particle-particle interaction are based on theoretical contact mechanics thereby enabling particles to be directly specified using realistic material properties such as friction and elasticity.The developed method was validated by comparison of numerical results with analytic solution and experimental data in the literature.Computational simulations have been conducted in three dimensions to model size-driven segregation phenomenon in aqueous suspensions.It has been illustrated that the proposed DEM/CFD method is a robust tool for analysing the microscopic behaviour of polydisperse liquid-particles system.