Abstarct: Stress dependent permeability is one of the most fundamental aspects of designing and evaluating nuclear waste repositories, extraction of oil and gas, ground water flow in dam foundation, Geothermal enrgy and etc. in this study the effect of confining stress and dilation angle on fluid flow and permeability of rock mass is evaluated using, Hybrid DFN-DEM Concept, by the use of geological studies of Parsian Earth Fill dam as case study. In order to do so by the use of Monte Carlo simulation method and with respect to Probability Density Function (PDF) of trace length and aperture of discountinuties the DFN of rock mass is created. The permeability components in x, y plane is calculated in 3D model by the use of 3DEC in different stress ratio conditions. The numerical results in this study showed that,with respect of simulation of the dialation process in joints, in the case of stress ratio of 2 or higher, the fluid flow and the rate of it, in models increases dramatically in x direction. However in y direction the situation is totally different and due to the existence of critical oriented joints, by increasing the stress ratio the permeability decreases. The change in rate of fluid flow through the discountinities in variety of stress ratios, dictate the critics of the critical oriented joints role. In order to validate the numerical analysis results in this study, the permeability components exctarcted from the numerical simulations were compared to Lugeon test values in the same site. To have a better analysis on results, the stress state in the site was estimated trough the use of world stress map and empirical methods, the estimations showed that the stress ratio in the area of study is in the range of 1 and 2, which is the sign of strike slip fault actions in the area. Comparing the maximum and minimum permeability components from numerical analysis with the Lugeon values from the site of study, in different stress ratios, showed that the Lugeon values are in the range of kmax and kmin from numerical analysis.