Abstract: In this paper, the significance of three-dimensional clasto-plastic analysis for complex rock foundation is pointed out at first. Then, by means of plastic theory , the relevant constitutive relationship; for concrete-rock materials and for weak intercalations in rock are selected respectively and their stiffness matrices are derived accordingly. Methods of solutions of such nonlinear problems are further briefly reviewed.A practical example of a gravity dam with weak intercalation in its foundation, using the program ROCKY5 compiled by the authors is presented. The displacements and stresses in the structure thus obtained are compared with those obtained by a simple elastic analysis.