In this study, theories of Discontinuous Deformation Analysis (DDA, Shi & Goodman, 1988) are employed to investigate the stability of rock slopes. Barton's shear strength formulation of the joint is employed to replace the Coulomb's formulation in the original Shi & Goodman's procedure. A field site is selected to provide the paramenters needed in the analysis. Dip and strike of the bedding plane are measured in the field. JRC, JCS, and are evaluated using the test result of the core drilled in the site. The analysis programs developed are verified with the field site.