Reflecting difficult problem of high pressurized Ordovician limestone water threatening deep coal mining, Yangdong Mine introduced advanced technology of horizontal directional drilling to carry out regional control on 8466 coal mining face. By studying key techniques such as how to find the Daqing thin limestone in fold and fault, how to drill efficiently after grouting and sealing, and so on, Yangdong Mine succeeded achieving the long-distance horizontal branch drillings in Daqing thin limestone which was only 5.5 meters thick. Based on advanced precision exploration of geological structure, grouting water structure and karst fissure zone, Daqing thin-layer limestone was strengthened. Two methods of geophysical prospecting and drilling were used to verify grouting effect to achieve purpose of sealing water channel and strengthening coal seam floor, which guaranteed safety mining of coal mining face.