Abstract:Assuming that the representative volumetric element(RVE) has three states,i.e. failure,damage and intactness. The damage can be expressed by degree of failure or intactness. The relation between stress-strain and density variation of rock crack has been obtained through the meso-damage theory and damage statistics model. By the Taylor method,the generalized consistent method and the Taylor medium method in the process of stress-strain,the variable rule of the crack density during the development process of rock stress-strain has been analyzed by examples. The variable characteristics of crack density at characteristic points and the influences of calculation methods have been discussed. Meso-damage theory is used to determine the residual strength of rock. It is shown that the nonlinearity of rock is the macroscopic behavior of development speed of crack density. Some other useful conclusions are also drawn.