Aiming at the problem of big drag during takeoff for seaplane, a hydrofoil seaplane with deflectable wings is proposed. The hydrodynamic lift generated by deflectable wing cutting the water surface during takeoff is big enough to lift the aircraft off the water surface. The deflectable wing can deflect the angle according to flight conditions during the flight phase. Aerodynamic and hydrodynamic coupling solutions and dynamic equilibrium equations are used to calculate the hydrodynamic performance for hydrofoil seaplane, and the aerodynamic characteristics of air cruise are analyzed. At the same time, the calculation of the same size double-float seaplane is carried out, and the hydrodynamic and aerodynamic characteristics for two configurations were compared. The numerical results show that the peak value of total drag for double-float seaplane is about 1.97 times of that of the deflection wing for hydrofoil seaplane during takeoff. Aerodynamic performance of deflecting wing with 0° deflection angle is optimal and the drag is lower than that of double-float seaplane during flight, which proves that the deflection wing layout of hydrofoil seaplane can effectively improve the hydrodynamic and aerodynamic performance for seaplane.