<p>The occurrence of mine floor water inrush accidents is mostly related to faults, i.e., water inrush accidents occur in impermeable faults in the natural state under the influence of factors such as mining and water pressure. Under the action of high water pressure in a fault fractured rock mass, the characteristics of the fault activation are not clear and definite, and the system of evaluating tectonic water inrush hazards under deep geological conditions has not yet been perfected. A typical reverse fault was used as the research background to conduct in situ water injection tests in two sites of this fault to explore the in situ hydraulics and permeability properties of the rock mass. During the testing of the fault rock’s permeability during three stages of change, the high-pressure fluid caused fracture expansion, resulting in a significant increase in the permeability of the rock mass. In addition, in different locations in the same fault, in the difference in the permeability is large.The research results show that the fault is a broken fracture rock type characterized by obvious anisotropy and heterogeneity. The results of this study increase our understanding of the permeability changes in tectonically fractured rocks under high water pressure and have guiding significance to practical coal mine production.</p>