Abstract: The 6th coal seam of the Carboniferous Permian in a coal mine in the Ordos Basin of Inner Mongolia is an extra-thick coal seam with an average minable thickness of 17.0 m. Its floor is threatened by limestone water. Distributed sensing optical fiber technology and cross-hole resistivity CT in situ comprehensive testing technology were used in the field, and the response characteristics of strain field and geoelectric field were obtained successively during mining. Combined with the threshold value of the discriminant parameter for loading deformation and failure of rock samples and detection section of practice, the monitoring data of the floor of four working faces in the mining area are analyzed comprehensively, and the detailed characteristics and evolution distribution law of the floor failure in the area are obtained. The floor failure has obvious zonation in vertical direction. It is believed that the floor failure depth of the working face in the mining area is 7.2-16.5 m, and the main damage layer is in the fine sandstone interval. The destructive disturbance zone is approximately 33 m deep, mainly in the sandy mudstone interval. The failure of the soleplate has a transverse leading stress effect, and the leading influence distance varies from 25 to 60 m. In addition, the damage characteristics of the floor in the study area are similar to a certain extent. The damage degree of floor caused by mining is spatially distributed in shallow areas in the northeast and deep areas in the southwest. The data obtained from the on-site test has a guiding role for the safe mining of the 6th coal seam in the deep part of the area and the prevention of water hazard.