Abstract: The mechanism of floor water-inrush at 10902 working face of Hebi Coal Industry Group thin coal seam is researched with the method of theory analysis and engineering calculation. The water-rich abnormal area at working face is studied with borehole verification and grouting reinforcement. The results show that the safety thickness of aquifuge is 10.5 m under the geological conditions, which is greater than the direct bottom sandy mudstone thickness of 9.15 m, and leads to the threat of water inrush at working face. Through the drilling and grouting reinforcement at water-rich abnormal area, water-inrush at working face reduced from 130 t/h before grouting to 20 t/h.