Abstract: Based on the fractal simulation of rock joints,numerical models for direct shear test of fractal rock joints were established,and the relationship between filling percentage and shear strength of fractal rock joints was studied by using the numerical simulation method.The results showed that the shear strength of fractal joints decreases nonlinearly as the filling percentage increased.When the filling percentage is less than 1,the shear strength of fractal joint decrease rapidly as the filling percentage increases,and the shear strength is controlled by the joint profiles and the mechanical property of rock and filling material.When the filling percentage is bigger than 1,the shear strength is controlled by the mechanical property of filling material,and the value of shear strength parameters approach to the value of shear strength parameters of filling material.