With the aid of damage mechanics and on the basis of statistical strength theory, a method for establishing the constitutive model of deep fractured rock mass is proposed and verified by laboratory and numerical tests. The fractured rock mass is divided into numerous micro-cubes. The strength of micro-cubes is related to the fracture degree and the strength of each micro-cube is randomly distributed. Thus the strength can be used to reflect the fracture degree of the rock mass. Among them, based on the fact that the work done by friction between fracture surfaces is equal to the strain energy released after the material fracture, the rock fracture degree variable defined from the mechanical point of view is obtained. In addition, it is assumed that the strength distribution of micro-cubes obeys the Weibull distribution and the stress behavior satisfies Hoek-Brown criterion. The constitutive model of fractured argillaceous sandstone rock mass is then established and verified based on typical triaxial test results of fractured rock samples. The results show that the calculated curve from theoretical model is in good agreement with the test results. At last, a supplementary numerical test is carried out using discrete element software PFC, which further proves the good calculation performance of theoretical model for argillaceous sandstone and the feasibility of the constitutive model establishing method proposed in this paper.