Abstract: Based on the non-linear deformation character of rock joints, a new constitutive model that describes the soften deformation after the peak is presented. The new model accounts for the stress decline due to wear and degradation under shear loading. And the traditional hyperbolic relation between shear stress and shear displacement is change into a softening curve. The dilation relation, which causes coupling of the normal and shear responses is modeled with a non-linear curve, rather than linear. The predicated results agreed well with the test results.