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In this study, the effect of the free surface on the supercavitating flow that surrounds a low aspect ratio wedge-shaped hydrofoil is studied based on computational fluid dynamics (CFD), with Cartesian cut-cell mesh method. The volume of fraction (VOF) method and the k -ε turbulence model with the Schnerr Sauer cavitation model are used for simulating the supercavitation in turbulent flow. Both quasi-3-D and full-3-D cases are considered. The quasi-3-D simulation results are compared with the previous water tunnel experimental data and analytical data, and the results agree well with each other. The results are presented for a wide range of submerged distance in terms of the free surface effect on the cavity shape, wave elevation and force coefficients. The range of the free surface effect is found. The simulation results show that the cavitating flow around the hydrofoil become shorter and thicker as the submerge depth decreases. As the aspect ratio of the hydrofoil studied in the full-3-D cases is low, the 3-D effect on the supercavitating flow is strong. The relationship between the flow patterns and vortex structures is also revealed from the numerical results.