Abstract: There are high head pressure in underground building and turnout pipe of pumped storage power station. The results of conventional pressure test can not reflect the permeability characteristics of rock mass under actual head pressure.In order to determine the permeability characteristics of rock mass under the action of high pressure water head, a high pressure water pressure test was carried out in the high pressure bifurcation pipe of a pumped storage power station. By studying the pressure-flow curve and the relationship between permeability and RQD, the critical pressure of rock mass was obtained, which provides a reliable basis for designing the selection of support in the bifurcation pipe lining.