Abstract: The joints and cracks of rock mass were considered as damage.The simulation method of joint network,damage mechanics and the theory of joint tensor were applied to analysis of equivalent shear strength parameters(i.e.,cohesion and friction factor).On the basis of analysis conclusion of rock mass damage mechanics,the approximate evaluation method of the damage variable in any spacial section was proposed.Taking the damage varible as weighted factor,the equivalent shear strength parameters of any spacial section were calculated in a weighted fashion with the shear strength parameters of intact rock and joints.The shear strength parameters of rock mass were fitted as orthotropic equivalent shear strength parameters by use of the spacial equivalent shear strength parameters.The computation codes of orthotropic equivalent shear strength parameters were developed and the example verification was carried out to test the rationality of the analytic results and the codes.