The process of water pressure caused by the confined water in the floor is mainly reflected in the water inrush of the floor rock. 9-101 working face of Pangpangta Mine was taken as example to study damage characteristics of floor, the evolution of floor stress distribution was got, disaster mechanism of confined water damage when bottom with fault structure was studied, it was considered that when the working surface advancing distance was 140 m, the floor damage depth was 12.5 m. The confined water would enter the goaf to form water hazards.