Based on the virtual internal bond (VIB) model

a fourth-order elastic tensor of the VIB evolution function is deduced. Two parameters in the evolution of VIB density are studied

and a numerical model of rock is developed under uniaxial compression. A general law of the influence of these two parameters on the whole stress-strain curve is obtained

and a stress-strain curve of homogeneous marble sample is simulated by the VIB model. Numerical results show that the stress-strain curve is in good agreement with experimental results. The applicability and feasibility of the VIB model for the constitutive relation of rocks are proved

which provides a new way to study the constitutive relationship.