In order to improve the effectiveness of early warning of water inrush from coal floor in thick coal seam and thin aquifer working face, 61303 working face of Tangjiahui Mine was taken as the research background, through high sensitivity microseismic monitoring technology, the continuous and dynamic fracture development range of floor failure depth during mining process was monitored. Through theoretical research and field monitoring, the energy, frequency and density of floor fracture microseismic events were analyzed. The degree determined the failure range of coal seam floor rock mass. The practice showed that the conclusion of high-sensitivity microseismic monitoring was in good agreement with the actual situation of production site. The microseismic monitoring provided an effective reference for continuous dynamic monitoring of floor failure depth.