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Direct shear test is commonly used for research and geotechnical engineering design due to its simplicity and cost effectiveness. However, analysis of many geotechnical structures such as earth pressure and slope stability problems require measurement of plane strain properties of soil. Therefore, it is usually relied on empirical relationships to predict soil properties in plane strain conditions from direct shear or triaxial tests. In this study, a two-dimensional plane strain numerical model is developed using the finite difference program, FLAC to simulate the mechanical behavior of sandy soil tested in direct shear box. Results are presented in terms of stress distribution within the soil specimen at different stages of shearing process and at different locations of the failure surface. Principal stresses and their directions are also investigated and discussed. Results indicated that, the plane strain properties of the sandy soil can be back-calculated from numerical simulation of direct shear tests with reasonable accuracy. Moreover, the numerical model was able to capture the trend in the experimental results and in most cases gave reasonable estimates of the shear strength and volume change of sandy soil. Numerical results also indicated that angle of internal friction at plane strain condition is significantly larger than the direct shear friction angle. In addition, both normal and shear stresses distributions at failure plane are diverted from being uniform at initial conditions to non-uniform during shearing process and at failure. Finally, principal stresses at failure surface are non uniform and rotated significantly during shearing process. [ABSTRACT FROM AUTHOR]