Abstract: The deformation and failure of rock masses are in general governed by the preexisting discontinuities and the local fissures induced by the state of stress, because these weak planes increase the deformability and reduce the strength of the rock mass. The mechanical properties of a rock system are thus determined by its interior structure and texture, as well as by the boundary conditions, such as the loading path, the constrained displacement and the geometry of the system.This paper describes a three-dimensional finite element model of the rock mass, where a fault underlain closely with or without a solf layer is dipping an angle of 60°or 90°between the fault plane and the horizontal axis. The external forces different in magnitude and direction are imposed at the boundaries, the effect of the intermediate principal stress, σ₂, on the concentrated stress level at the fault tip is studied as well.Numerical results similar to that of both the field and the laboratory tests confirm that present model provides physically measurful simulation and thus can be used to study the stress distribution of a geological body under different boundary conditions and thus to evaluate the geological background causing a huge earthquake.