<p>In recent years, it has been pointed out that there is a relative aquifuge in the top portion of the Ordovician limestone aquifer. To further explore the water-resisting property of Ordovician limestone, systematic tests were conducted on the O-7 borehole samples, including well logging curves analysis, physical and mechanical property tests, X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM). The results confirmed the existence of the relatively aquifuge. Compared to conventional Ordovician limestone samples, the presence of minerals such as kaolinite, a large proportion of micropores, and the filling of fissures under the microscopic structure jointly revealed the mechanism of enhanced water-resisting property: macropores and fissures were filled by weathering substances and decomposed into mesopores or micropores, thereby forming an impermeable texture in the rock, and thus creating an impermeable structure on a large scale. Based on the quantified thickness of the aquifuge, the potential risk of the lower coal seam mining in Yangcun Coal Mine was assessed using the water inrush coefficient method. The existence of the aquifuge would expand the field coverage of the mining safety zone. This indicates that the existence of the aquifuge and further quantification has great practical significance for reducing the management cost of the Ordovician limestone aquifer and raising the mining limit.</p>