Based on the current research on constitutive model of rock-soil mass, a new constitutive model is developed. It can describe the four different behavior characteristics of rock and soil, including elastic-plastic softening, elastic-plastic hardening, perfect elasto-plastic, elastic fragile. There are four parameters of new constitutive model. The existing constitutive models such as Duncan-Chang model are only a special case of the proposed constitutive model. Its parameter calibration is performed. The basis of constitutive model parameters calibration is that the correlation coefficient between the behavior characteristics described by the new constitutive model and experiment data is located in the optimal state. The behavior characteristics of post failure of rock-soil mass are analyzed, it is found that the behaviours of post failure of rock-soil mass can be described with quasi stress-strain relation. The experiments are used to verify the applicability of the developed model. The results show that the model is suitable to describe the behavior characteristics of rock-soil mass and can provide a reference for research on virtual internal bond model, spring model and discrete element method, etc.