Hydrocyclones are commonly used liquid-solid separation devices in the mining, metallurgy, and energy industries and are known for their high efficiency and ease of maintenance. In this study, computational fluid dynamics (CFD) is used to investigate the impact of particle size distribution (PSD) width on the behavior of fluid and particles within a hydrocyclone. After validation of the reliability of the numerical model with experimental data, the fluid-solid flow characteristics are discussed. Key findings indicate that the PSD width significantly influences the pressure drop, separation efficiency, and particle behavior. The overall separation efficiencies for PSD widths of 0.1, 0.3, 0.5, and 0.7 are 68.4%, 65.5%, 56.2%, and 47.6%, respectively. A rise in the PSD width brings about a higher pressure drop and an enhanced tangential velocity. At a PSD width of 0.1, the separation efficiency is maximized, and the pressure drop is minimized. A wider PSD distribution leads to a higher number of internal vortices and an increased flow complexity. These findings provide valuable insights into the separation mechanisms of hydrocyclones, contributing to the design and optimization of these devices for improved performance.