Abstract: The hydro-mechanical coupling of fractured rock mass is a hot research focus at home and abroad recently. The fractures(or joints) of the rock mass play the main pathways of the fluid flow in fractured rock masses. The apertures of the fractures play an important role in the fluid flow. Both the shear stress-induced dilations and the normal closures or openings induced by normal stress can change the fracture apertures. The permeability of fractured rock mass by taking in account the shear dilation is studied in this paper. It uses the UDEC. The realistic discrete fracture network of sandstone is generated using the joint information from the in-situ survey and the Monte-Carlo Method. The permeability changes of the fracture network rock are simulated by increasing the stress ratio RS(RS=horizontal stress/vertical stress) while keeping the vertical stress constant. The shear dilation of the fractures are considered using the Cloumb slip joint model. The results show that all of the hydraulic apertures, the fluids velocity and the permeability coefficient of the fractured rock mass decrease with the increment of the stress ratio during the stress ratios are enough small(RS is small than 3.1). However, they increase with the increment of stress ratio when the stress ratios are enough large to cause the shear dilation of the fractures(RS is large than 3.1). When the stress ratio is large enough, both the overall permeability and flow patterns are controlled by the fractures which are observed to have shear slipping and dilation phenomenon. During the stress ratio increase from 0.5 to 3.1,the permeability coefficient of the fractured rock masses considering the joint shear dilation is the same to that of disconsidering joint shear dilation. It shows that no shear dilation appears in the fractured rock masses when the stress ratios are enough small. When the stress ratio is more than 3.1,the permeability of rock masses considering the shear dilation increases significantly, but that of disconsidering shear dilation joints decreases slowly. The former is about 2～3 orders of the magnitude more than the latter when the stress ratio exceeds 3.1. The results show that the shear-induced flow channeling has very important impact on the permeability of the fractured rock mass, which shouldn't be neglected.