Abstract: The utilization of underground water resources in coal mines is an important way to realize the sustainable development of mining areas, and it is also a key measure to protect the ecological environment and alleviate the shortage of water resources.In this paper, the mine water of Sangshuping No.2 well is taken as the engineering background.By collecting the underground water samples and testing the chemical composition, the chemical types of mine water are determined, which are mainly HCO₃-Na and HCO₃（Cl·SO₄）-Na, showing alkaline and high salinity.In order to explore the influence of different particle sizes of coal in goaf and the porosity of coal on the removal effect of suspended solids in mine water, the indoor precipitation experiment was designed, and the control group experiment was designed.The results showed that after 65 h precipitation, the suspended solids content under different particle sizes was reduced by more than 70% compared with the initial value.Under the same particle size, the suspended solids content of the experimental group was less than that of the control group glass beads.Therefore, it is considered that the particle size is negatively correlated with the purification efficiency, while the adsorption degree is positively correlated with the purification efficiency.Finally, the mechanism of suspended solids removal in coal mine goaf is analyzed, including filtration, sedimentation and adsorption.