Abstract: Accurate knowledge of the 3D surface dynamic contact characteristics is the basis for the evaluation and prediction of shear behaviors of rock discontinuity. Firstly,the INTERFACE model of the FLAC3D software was modified using the FISH language to accurately represent the mechanical behaviors of rough rock discontinuities during shear. Then,using numerical simulation and indoor experimental methods,the distribution of contact area and shear stress on the surfaces of discontinuities in shear and its evolution characteristics were studied,and the effect of normal stress and joint roughness coefficient roughness (JRC) on the contact characteristics was analyzed. Finally,the relationship between surface morphology,contact characteristics and shear stress was investigated to reveal the mechanism of shear stress evolution of rock discontinuity. The results show that due to the over high cohesion and normal stress caused by the surface bulges that cannot be chewed off,the FLAC3D self contained INTERFACE model cannot simulate the post peak shear behaviors of the rock discontinuity well. The failure behaviors of the rock discontinuity can be well simulated by correcting the cohesion and normal stiffness of the damaged INTERFACE elements. With the increase of shear displacement,the contact area of rock discontinuity decreases gradually,while the maximum penetration depth increases. With the increase of normal stress,the contact area and penetration depth increase. With the increase of JRC,the contact area decreases and the maximum penetration depth increases. With the gradual decrease of the contact area of the rock discontinuity in the shear process,the shear stress concentration phenomenon becomes more obvious. When the INTERFACE elements reach its maximum shear stress,the distribution range of maximum shear stress increases. With the increase of the normal stress,the distribution range of shear stress increases,and the distribution range of the high shear stress also increases. With the increase of JRC,the contact area decreases,while the distribution range of high shear stress increases significantly. The critical apparent dip angle is an important parameter to assess the contact area of the rock discontinuity. The critical apparent dip angle increases with the increase of shear displacement,and its increase rate gradually becomes slower and shows a power function relationship. The critical apparent dip angle decreases with the increase of normal stress,and increases with the increase of JRC. There is a strong correlation between the change of shear stress and the contact area of the rock discontinuity. The decrease rate of the contact area ratio is different in different shear displacement stages. The decrease rate is the fastest in the elastic stage,followed by the displacement softening stage,and the decrease rate is the slowest in the residual strength stage.