Abstract: In the three dimensional analysis of rock mass with FEM, in order to consider the nonlinear meshanical behavior of rock block （including joints and cracks） and the weak fabrics （faults,weak intercalations） in rock mass, assuming the rock mass to be an elasto-plastic body approximately, two general mechanical models for the rock block and the weak fabrics in rock mass are suggested respectively. And in the light of the non-associated flow rule in plasticity, constitutive equations corresponding to the suggested models are developed.