Abstract：Based on the technology of three-dimensional joint network simulation and superposition principle of seepage energy，the calculation method is presented to determine the three-dimensional permeability tensor and the representative elementary volume(REV) size of fractured rock masses. The method is feasible and reasonable to calculate permeability tensor of fractured rock masses considering the distribution and connection of joint network and the influence of aperture changes(decided by stress fields) on permeability tensor according to cubic law. The factors influencing the permeability characteristic and REV size of rock masses such as trace length，space，aperture，inclination and the number of joint sets are discussed. As an example，the permeability tensor and REV size of fractured rock masses on the right bank of Laxiwa Hydropower Station are studied. At the same time，the stress-dependent permeability issue is investigated. The results is worth using in engineering design.
