Abstract: The height of water flowing fractured zone is hard to determine. In order to have a more in-depth understanding on its guide rising mechanism, rock fracture formation and expansion will be studied. The result shows that the depth of original fissure is limited, which is mainly related to the pressure of the confined water. Crack propagation is very complex, but it mainly caused by ground stress, confined water pressure, the crack angle. The greater of the water pressure and the inclination of crack angle, the easier upward development of the crack. The water flowing fractured zone is more easily run through the floor failure zone with the increased probability of sudden water inrush.