Abstract: Coal mining under pressure is an important mining technology to extend mine service life, reduce resource waste and ensure energy security. However, this mining method faces the threat of floor water inrush, requiring floor grouting to guarantee the water-resisting performance of the floor. Clarifying the seepage law of grout in fractures is a key scientific issue for selecting reasonable parameters such as grouting borehole layout and grouting pressure. Taking the F6226 high-intensity fully mechanized caving face of Buliangou Coal Mine as the engineering background, this study first adopted the “Five Maps-Dual Coefficients Method” for water inrush risk zoning and delineated high-risk areas of water-conducting structures. Secondly, based on scanning electron microscope (SEM) and X-ray diffraction (XRD) experimental methods, the microstructure and mineral composition of floor rock samples were analyzed. Then, based on 3D laser scanning, the fracture surface roughness of 5 types of floor rock samples was calculated. Finally, a grouting test device for single-fracture rock mass of coal seam floor was developed, and grout seepage tests in fractures were carried out to master the relationships between grouting pressure, grout flow rate, roughness and water-cement ratio. The results show that under the condition of fixed water-cement ratio, the grout flow rate increases with the increase of grouting pressure, and the growth rate accelerates with the increase of the pressure; under the same grouting pressure and roughness condition, the grout flow rate is positively correlated with the water-cement ratio; the grout flow rate in fracture areas with higher roughness is significantly lower than that in areas with lower roughness. Based on the above laws, floor fault grouting engineering practice was carried out in the F6226 working face. Radio wave penetration technology was used for detailed exploration of high-risk areas to locate specific water-conducting structures. By optimizing grouting pressure and water-cement ratio parameters, water-conducting channels were successfully blocked, realizing safe mining of the working face.