Based on the basic features of rock mechanics in a coal mine and combined with the fundamental characteristics of the micro structural features of the rock under microscope, the variation of acoustic velocity and amplitude of acoustic waves are measured when the rock is under loading. Several stages of fracturing of the rock are identified. As a result, the rock failure can be predicted. In the meantime, from the basic viewpoints of rock fracture mechanics, an insight is made into the mechanism of floor heave water in coal mines.