Abstract: The stability of a dense-medium suspension is a key factor affecting the separation efficiency of dense-medium cyclones. To elucidate the coupled effects of suspension density, magnetite particle size, and coal slime content on the stability of dense-medium suspensions during preparation, a combination of computational fluid dynamics (CFD) numerical simulations and sedimentation tests was employed to investigate the static sedimentation characteristics of magnetite–coal slime suspensions. The CFD simulation results showed that 10 μm magnetite particles exhibited a relatively slow and gradual settling process, characterized by a uniform compaction settling mode. In contrast, the settling rate of 20 μm magnetite particles increased significantly, resulting in a distinct two-phase stratification characterized by a clear supernatant layer and a bottom sediment layer. An increase in the mass fraction of coal slime significantly improved the stability of the suspension system. The sedimentation test results indicated that when the suspension density increased from 1.25 g/cm³ to 1.35 g/cm³, the settling time increased from 15~20 min to 30~35 min. When the proportion of magnetite particles smaller than 0.045 mm increased from 85% to 95%, the settling time increased from approximately 15 min to 20~25 min. When the proportion of magnetite powder drops from 60% to 40%, the settling time exhibited a nonlinear trend, first decreasing and then increasing. Both suspension density and magnetite particle size showed significant positive correlations with settling time. Adjusting the magnetite particle size, suspension density, and coal slime content can effectively regulate the static sedimentation characteristics of the suspension system, providing a reference for the precise preparation and control of dense-medium suspensions in industrial operations.