An elasto-plastic constitutive model for rock interface is proposed based on a stress history vector. The stress history vector is used in order to express both strain hardening and strain softening characteristics of rock interface. The applicability of the proposed constitutive model is examined by means of a finite element analysis. A comparison between the numerical results and the experimental results on mortar interface is carried out. It is found that the proposed constitutive model can simulate both strain-hardening and strain-softening behaviors of rock interface.