Abstract: The mechanical effect of occurrence of discontinuities is an important aspect in determination of strength and deformation behaviors of rockmass. This paper presents the test results on the discontinuities. Factors effecting the deformation of rockmass, including discontinuities and structural mass, are analyzed. The compression shear zone and tension shear zone are formed in the rock mass, and their causative mechanisms are revealed. The mechanical effects of the occurrence of three sets of discontinuities are studied in detail in this paper.