Abstract: Multiple discontinuities exist in the natural rock mass and these discontinuities are geometrically rough. In this paper,a rough discrete fractures network model (RDFN) considering the complex and rough geometry distribution of discontinuities is introduced and tested under direct shear test using PFC2D. The corresponding shear behaviors, such as shear strength,shear modulus and failure pattern,were studied and compared with the traditional linear dis- crete fractures network ( DFN) model. Numerical results show that fracture surface roughness can significantly affect the shear behavior of rock masses. The peak strength and shear modulus of the RDFN model are ralatively higher than those of the DFN model. The principal shear fractures in the DFN model mainly coincided along the linear joints. Parts of the intact rock elements were fractured. The failure pattern of RDFN model is much more complex and more intact rock elements were fractured after peak shear strength. The peak shear strength and modulus of all jointed rock models decrease with the increase of sample sizes. The value of shear modulus of the RDFN model is higher than that of the DFN model. The values of shear strength tend to be stabilized with the scale size reaching 4. 0 m according to the scale effect analysis.