Abstract:On the basis of analyzing the characteristics of rock mass deformation and general rheological models,a new non linear viscous substance which is related to stress state and time is presented. When the stress is lower than its limit value,the deformation of the new nonlinear viscous substance will reach to the stable state as time going on,otherwise,the deformation will increase sharply. The new nonlinear viscous substance is applied to improve the function of the classical Maxwell model. A new visco-elasto-plastic constitutive model consisted of 5-components (VEP-5C model) is defined in series with the improved Maxwell model,the classical Kelvin model and the St. Venant plastic substance. The elastic component and the non-linear viscous component of the improved Maxwell model can simulate the instantaneous elastic deformation and visco-plastic deformation respectively. The Kelvin model and St. Venant component of VEP-5C model can represent the visco-elastic deformation and instantaneous plastic deformation respectively. Theoretical analysis and results of test indicate that the new 5-components visco-elasto-plastic constitutive model can fully describe the characteristics of rock mass deformation. The new model can also characterize the property that the rock mass rheological deformation will keep stable in lower stress state,while accelerating rheological deformation in stress exceeding its limit.