An improved model of tangential contact stiffness for joint interface was put forward by using anisotropic fractal geometric theory. Numerical simulation was executed to visually attain the complex nonlinear relationships between joint interface tangential contact stiffness and normal load, tangential load, fractal dimension D, fractal roughness G, relating factor K and material property φ. The numerical simulation results indicate that the joint interface tangential contact stiffness increases with increasing normal load, relating factor K or material property φ, but decreases with increasing tangential load or fractal roughness. When fractal dimension is smaller, the joint interface tangential contact stiffness increases as fractal dimension increases. However, when fractal dimension becomes larger, the joint interface tangential contact stiffness decreases as fractal dimension increases.