Hydrocyclones are widely used in various industries to classify particles mainly by size. In this work, two numerical models are developed to model the multiphase flow in hydrocyclones: one is a combined approach of volume of fluid (VOF) model and discrete element method (DEM) with the concept of the coarse-grained (CG) particle (CG VOF-DEM); the other is a combined approach of the Mixture model and DEM model with the CG concept (CG Mixture-DEM). The simulation results show that the CG VOF-DEM model is quantitatively applicable to relatively dilute flows while only qualitatively applicable to dense flows. On the other hand, the CG Mixture-DEM model can be quantitatively applicable to both dilute and dense flows. The work suggests that the CG Mixture-DEM approach could be a useful tool to estimate the performance of hydrocyclones.