Abstract: The elastic energy accumulates in the hard rock stratum with whole blocky structure because of underground mining. The hard rock stratum will fail with the increase of the elastic energy and instantaneously release massive energy of motion, which induces high water pressure in the aquifer near the hard rock stratum. The high water pressure creates the water-conducting which is impacted instantly between the aquifer and excavation free face so as to form the dynamic water inrush. Haizi Coal Mine is taken as a case study. The geological conditions and main factors of separation layer water are analyzed based on field investigation and numerical simulation. The burst tendency indices ( Dt, W_ET and K_E ) of the hard rock stratum are tested. The excess hydrostatic pressure under the action of the impact dynamics is obtained by the relevant tests. Thus, the formation mechanism of dynamic impact failure zone is preliminarily studied based on the theory of blasting dynamic mechanics.