Abstract: Unauthorized mining in coal pit is common in China's coal industry. As the scope of unauthorized mining and the amount of accumulated water are hard to determine, the goaf water seriously threatens the safety of mining in adjacent large coal mines. In order to explore the unauthorized boundary of coalpits quickly and accurately and prevent the threat of goaf water, the long distance drilling technology of ground bedding borehole in medium and thick coal seam is proposed based on the controllable trajectory and accurate positioning of ground directional drilling, which mainly includes precise drilling in extremely soft and medium-thick coal seam, drilling fluid ratio of different lithology, prevention and plugging of lost circulation in goaf. In addition, the prevention and control process of water disaster in the goaf of the unauthorized mining area is put forward. Taking the right side of Ⅲ63 mining area of a coal mine in North China coalfield as the research area, adopting the goaf water disaster prevention technology system in the unauthorized mining area, the unauthorized mining boundary and direction are accurately identified through engineering demonstration, which provides a basis for reasonably retaining the waterproof coal pillar in the mine boundary. The successful application of the method provides a scientific technique for the prevention and control of goaf water disaster in similar mines, and provides valuable experience for the ground bedding borehole in the field of detecting the unauthorized mining boundary and gas extraction from extremely soft coal seam.