Abstract: The deformation of rock mass is considered as the summation of the linear elastic deformation of intact rock block and nonlinear elastic deformation of joints. On the basis of deformation characteristics of joints, a new constitutive model for normal displacement of joints is presented. It considers the influence of the initial stress state on the deformation. The computation method for jointed rock mass equivalent strain is studied by use of the joint network and the theory of equivalent continuous strain. According to the elastic orthotropic constitutive model, the rock mass is regarded as orthotropic continuous material, and the orthotropic equivalent deformation parameters are computed. The computation codes of orthotropic equivalent deformation parameters are developed. The example verification is carried out to test the rationality of the analytic results and the codes.