In this study, the governing equations and methods in the design of the geosynthetic reinforced soil walls for providing both internal and external stability of these systems have been presented in an appendix at the end of this thesis. Since these design methods, are based on a limit equilibrium approach, the exact distribution of stress and strain within the reinforcements and the wall face deformations could not be obtained. Therefore, the next part of this research study has been devoted to the numerical analysis of geosynthetic reinforced soil walls using FLAC3D software. The aim of these numerical analyses is to study the internal behavior of these structures to acquire an optimal performance. To achieve this aim, an attempt has first been made to evaluate the effect of various design parameters in direction of a parametric analysis. The effect of reinforced block geometry, consisting of reinforced block with inclined face and inclined reinforced block (rotated reinforced block) has then been studied to achieve the optimum performance of these systems. Doing numerous modeling and analyzing, it was determined that inclining of wall face largely improves the performance of these systems (including a reduction in wall face horizontal deformation, stress and strain distribution of reinforcements, and backfill surface settlement). But reinforced block rotation around axis Y (perpendicular to wall cross section) to a 12 degree angle, shows more improvement in the performance of these systems, so that the maximum reinforcements forces is reduced up to almost 44 percent. Finally, the analyses results made it possible to introduce an optimum inclination angle for reinforced block in which fewer reinforcements may be used in comparison to the horizontal reinforced block while both have the same performances. In addition, considering wall sliding stability in three cases of horizontal reinforced block, reinforced block with inclined face and rotated reinforced block, it was found that limited rotation of wall face and reinforced block causes the system sliding stability to be improved. Keywords: Reinforced soil, Geosynthetic, Reinforcement, Rotated reinforced block, Inclined face