In order to research the deformation and failure characteristics of floor in fully mechanized caving mining for extra-thick coal seam in Yanzhou Coal Field, the strain induction method, borehole imaging technology and numerical simulation and theoretical method are used to comprehensively analyze the failure characteristics of floor for mining extra-thick coal seam in 1305 working face in Dongtan Coal Mine. It is found that the measured results of strain induction method reflect the mining pressure action law on floor in horizontal and extended depth directions have a good agreement with borehole imaging technology, it is found that the deformation and failure of the floor are most severe after the working face is pushed over a certain distance. On this basis, the engineering geological numerical model and theoretical model of working face mining are established, and the deformation and failure depth of floor is determined by the development characteristics of plastic zone at different depths of floor. According to the strain induction intensity of floor, combined with the numerical simulation analysis and theoretical analysis, the range of floor mining failure depth of 1305 working face was obtained. The research results and metheds have important practical reference value for the similar geological and mining conditionsthe mining safety support of extra-thick coal seam and the prevention and control for water inrush from mining floor.