Aerodynamic and hydrodynamic coupling solution and dynamic equilibrium equations were used to calculate the hydrodynamic performance for hydrofoil seaplane during takeoff. Realizable k-e model was used to calculate NACA0012 three-dimensional ground effect wing and verify the aerodynamic calculation method. The VOF method was used to simulate the validation model under different Froude numbers to verify the hydrodynamic calculation method. Finally, the takeoff process of hydrofoil and double-float seaplane was numerically calculated. The results show that the hydrofoil can generate some hydrodynamic lift. When the speed reaches 12 m/s, the hydrodynamic lift generated by hydrofoil lifts the fuselage off the water surface; The peak hydrodynamic lift of hydrofoil is 6395 N, which accounts for 83% of the total lift of seaplane, and the drag of the double-float seaplane increases rapidly, and its peak drag is about 1.87 times that of the hydrofoil seaplane, which proves that the hydrofoil can generate large hydrodynamic lift and effectively reduce the hydrodynamic drag of the seaplane.