Abstract: The opening of an underground coal mine reservoir provides an effective technical approach to ensure the rational utilization of water resources during mining operations. This study focuses on the rock and mine water of the Daliuta Coal Mine reservoir in the Shendong Mining Area, employing simulation tests for mine water suspended solids removal and a coupling simulation of Fluent-EDEM. The impact of rock accumulation on the removal of suspended solids in water is quantified, revealing that the accumulation environment alters the mine flow state, creates a distinct reflux zone and low-speed zone, extends the sedimentation distance for suspended matter, and reduces water flow disturbance, resulting in a quasi-free sedimentation environment. Within a specific range, the suspended matter concentration gradually decreases with increasing settling time and distance. At the m outlet, the suspended matter concentration is 20 mg/L, a 95.7% reduction from the initial concentration. The steady-state settling time for suspended matter is 5 hours, with a turbidity of 60 NTU, significantly smaller than the 9 hours and 350 NTU observed in the blank simulation test. Post-sedimentation, the average diameter of suspended particles decreases from 14.99 µm to 2.02 µm, while the specific surface area increases from 12.30 m²/g to 15.75 m²/g. The removal of suspended matter from the underground reservoir is primarily through filtration, sedimentation, and adsorption, which results in a shorter sedimentation time and more efficient removal of suspended matter. This research provides a theoretical foundation for predicting effluent quality characteristics and preventing and controlling siltation in coal mine underground reservoirs.