Abstract: In order to investigate the numerical method for transient flows around a pitching hydrofoil, the numerical simulations for a NACA66 hydrofoil are performed by using the standard k-ω SST turbulence model and revised γ-Re_θ transition model respectively. The simulation results are compared with the experimental results, and the hydrodynamic property and the fluid structure during the pitching process are studied. It is revealed that, compared with the standard k-ω SST turbulence model, the revised -Re transition model is able to present the hydrodynamic property and the fluid structure of the transient flow around a pitching hydrofoil more accurately, and better predict the separation and transition process in the boundary layer. The transient flow process around a pitching hydrofoil can be divided into 5 parts. At small angle of attack, transition is observed at the leading edge of the foil, resulting in the inflection of dynamic property curves. As the angle of attack increases, a clockwise trailing edge vortex expands toward the leading edge of the foil. At high angles of attack, large-scale load fluctuations are observed due to the stall caused by separation of the leading edge vortex. The transition from turbulent flow to laminar flow occurs during the downward pitching process.