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Due to high water pressure on deeply buried coal-seam stope floors, the primary voids in the rock mass can easily expand and connect under the actions of water pressure and mining. This can form a vertical water passage that increases the risk of water inrush accidents at the stope floor. At present, many coal mines in eastern China adopt advanced regional ground grouting to transform aquifer floors or reinforce aquicludes to control confined water. However, there are some problems such as the low filling rate of primary micro-voids and ineffective grout diffusion along the vertical macro-fractures of the stratum, which seriously reduce the grouting effect. Given the above problems, we combined macroscopic and mesoscopic sacle characteristics of pore development in the top stratum of the Middle Ordovician limestone (MOL), which is the target stratum of coal-seam floor advanced grouting in the Hanxing mining area. Macroscopically, based on drilling fluid consumption and field outcrop development of the MOL, the macro-scale vertical porosity development characteristics of the MOL stratum were analyzed. At the micro-level, micro-computed tomography was used to scan rock samples from the top of the MOL to quantify the development characteristics and geometric parameters of the voids. The results show that, macroscopically, the Fengfeng Formation at the top of the MOL in the Hanxing mining area has good water yield, but the horizontal and vertical distributions are not uniform and the water yield increases or decreases with burial depth. Microscopically, the locally developed part of the rock samples showed good vertical connectivity, and the plane porosity of the rock samples was concentrated within ranges of 0.40–5.12% and 6.8–15.28%. Most pores had equivalent diameters of less than 200 μm and the volume proportion was more than 2000 μm. In the fractures, closed fractures and micro-open fractures were most common, with stable average widths of 120 μm and 420 μm, respectively. Medium-tension and wide-tension fractures accounted for a relatively small proportion of the fractures in the rock samples, which had good ductility. [ABSTRACT FROM AUTHOR]