Hardening and softening properties of the materials is described by introducing plastic internal variables to hardening function in most softening constitutive models of rock

without considering the damage effects of micro-crack growth and different performances of initial yield strength f0 and yield limit fu between the uniaxial tensile and compressive loadings. Plastic yield criterion is used simultaneously with the damage criteria to simulate the physical behavior of rock-like materials based on D-P criterion

and elastoplastio damage constitutive model with its numerical algorithm is also proposed. Borja’s hardening/softening strain function is employed as the plastic yield function

indicating the plastic internal variables and stress states are two important factors to the hardening function. Volume expansion caused by micro-crack growth is responsible for rock damage evolution D

which can be characterized by proposed function of volumetric strain. The code of elastoplastic damage constitutive model of rock is implemented using return mapping implicit integration algorithm. The proposed model is used to uniaxial tensile and compressive tests and the results agree well with the characteristics of rock-like materials and experimental curves.