No. 8 coal seam recovery mining threatened by limestone water, in order to accurately get the possibility of water inrush, through theoretical calculation and numerical simulation analysis, the mining dynamic pressure and confined water pressure under the influence of plastic failure depth of floor strata was studied. The plastic failure depth of floor was settled during the working face recovery mining, and the water inrush coefficient method was adopted to analyze, with convince that water inrush accident was easy to occur during the working face recovery mining. The results of field application showed that this method successfully improved the strength of waterproof layer and realized safe and efficient mining of working face.