Abstract: To improve the thickening effect of the suspension and the separation density in the first stage of a traditional pressureless three-product heavy medium cyclone (HMC), the original cylindrical structure was modified into a cylinder-cone (cone angle 1.91°)-cylinder structure. Computational Fluid Dynamics (CFD) numerical simulation methods and Fluent software were employed to simulate the internal flow field of the HMC, obtaining the distribution of the internal pressure and velocity fields in both the first and second stages. The research results indicate that, compared to the cylindrical structure, the improved cyclone maintains higher internal pressure in both stages. This allows for a reduction in feed pressure and energy consumption while still meeting separation precision requirements. Additionally, the lower pressure leads to reduced rotational speed, thereby mitigating internal wear and extending the equipment's service life. The tangential velocity remains high within the first-stage conical section, providing sufficient centrifugal force to enhance the thickening effect; meanwhile, the tangential velocity in the second stage shows no significant change. The axial velocity is higher in the inner helical region of the first stage, which facilitates faster discharge of lighter products and increases throughput. In the second stage, the axial velocity in the inner helical region decreases slightly, maintaining a minimum processing capacity even under reduced maximum throughput conditions. In conclusion, the improved pressureless three-product heavy medium cyclone can effectively enhance both the thickening effect and the separation density of the first-stage cyclone.