One of the most popular methods for improving weak soil properties is soil reinforcement with geogrid-layers, the geogrid-layer increases the low shear resistance of fine sand. The Abaqus 3-D model is utilized to simulate large-scale direct shear apparatus. Numerical models are conducted on geogrid-reinforced fine sand to estimate how geogrid-axial stiffness affects the shear strength behavior. Shear parameters, shear strength ratio, internal shear coefficient, and mobilized geogrid tensile strength are studied in both longitudinal and transverse directions. The steel box for large-scale direct shear consists of two separate parts with dimensions of 200 mm x 200 mm x 100 mm. A geogrid-layer with different axial stiffness between 200 kN/m and 1000 kN/m with an increment of 100 kN/m is fixed between the two separate parts to estimate the shear resistance increase of geogrid-reinforced fine sand. The shear strength of geogrid-reinforced fine sand increases with geogrid-axial stiffness; for the fine-sand elastic modulus of 10 MPa, the shear strength ratio (SSR) increases from 1.80 to 3.10 when the geogrid-axial stiffness increases from 200 kN/m to 1000 kN/m. However, the (SSR) values decreased with increasing fine-sand elastic modulus, the (SSR) values were 1.0 and 1.60 for the variation of geogrid-axial stiffness from 200 kN/m to 1000 kN/m when the fine-sand elastic modulus increased to 40 MPa. The most economical and optimal values of geogrid-axial stiffness are 500 kN/m and 300 kN/m for fine-sand elastic moduli of 10 MPa and 40 MPa, respectively.