Abstract: Taking the floor damage of mining face above confined water of Zhaogu No.2 Coal Mine 11050 working face as the research object, by developing a experimental platform for simulating the relationship between confined water loading and floor failure, we carry out physical simulation of confined water on mining face and observe rock characteristics and analyze the results by ultrasonic testing instrument. The results show that a crack in the rock strata experiences the development process of generation, extension, run-through, with the advance of working face, which eventually determines that the damage depth of floor fracture is 16 cm.