Abstract: The three-dimensional model for a randomly packed bed filter was established by the combination of computational fluid dynamics (CFD) and discrete element method (DEM). To obtain more reliable simulation results, the liquid-solid, particle-granule and particle-particle interactions were all taken into consideration. The filtration performances of the system including filtration efficiency, pressure drop and impurity holding capacity were systematically analyzed, and the particle deposition distribution and morphology were quantitatively studied. The simulated results of filtration efficiency agreed well with those obtained from experimental operations. The deviation of the pressure drop fell in the allowable error range of the Ergun equation. The impurity holding capacity could be represented by the deposition uniformity obtained by simulation, which increased with superficial velocity. Correlation of deposition uniformity for granular bed filters was also simulated with a good prediction accuracy. The results show that cascade filtration has both a high filtration efficiency and a low pressure drop by combining deep bed filtration and surface filtration. The quality factor of the cascade filters is greater than those with single-layer filters. Simulation of particle deposition morphology and distribution suggests that the particles mainly deposit on the surface of single-layer filter packed with fine granules, resulting in a small holding capacity. As for the cascade filter, the fine and coarse granular layer produces a high filtration efficiency and large impurity holding capacity, respectively