The cavitation inception of a two-dimensional hydrofoil is studied numerically by using the unsteady Reynolds averaged Navier-Stokes method that includes a cavitation model explaining the phase change between the water and vapour. The cavitation inceptions of the NACA0022 hydrofoil at various angles of attack are estimated after following the dependence tests of grid and turbulence model on the wetted flow around the NACA0012 section. In this paper, cavitation inception is determined when the computed cavitation volume approaches to zero value by gradually increasing cavitation number. In the numerical results, the computed sheet cavitations attached to the suction side of the hydrofoil show a close agreement with the cavitation observations in the KRISO medium-sized cavitation tunnel. Finally, the cavitation inception bucket predicted by the current cavitation simulation shows a better agreement with the experimental data than the two results of the potential flow and the minimum pressure analyses.