Large part of deformation and failure of rock masses are governed by both characteristics of geometrical distribution of discontinuities and those of mechanical behavior in a single discontinuity in slopes, foundation ground and caverns. It is thought that stability of those rock structures extremely depend on not only existent discontinuities but also new cracks which are generated and progress due to loading or excavation. In this paper, a new approach is proposed for modeling generation and progress of cracks due to shear and tension failure in the matrix by using distinct element method. Next, appropriateness of the approach are verified by means of comparison with result of theoretical analysis for the problem of cylindrical hole and bearing capacity of strip footing on slope. As applications to field problems for discontinuous rock masses, simulation of underground opening excavation and footing of bridge on slope are also carried out.