The invention provides a floating semi-active swing hydrofoil tidal current energy catching device; and the device consists of two sets of crank and rocker mechanisms, wings, synchronous belts and belt wheels, a control motor, an acceleration mechanism, flywheels, floating cylinders, flat plates, a generator and corresponding transmission parts. The vertical swing motion of hydrofoils is converted to the one-way rotation motion of cranks through the transmission of the crank and rocker mechanisms; and after the acceleration mechanism speeds up, the energy is finally transferred to the generator to realize the energy conversion. The motor is used for realizing the real-time control of wing swing angle motion rules; the rotation inertia of the flywheels is used for overcoming the dead point problem in the motion of the crank and rocker mechanisms; and the acceleration mechanism is used for raising the rotation speed into a rated rotation speed range of the generator. The device realizes the energy conversion by using the motion characteristics of the crank and rocker mechanisms, and actively controls the hydrofoil attach angles by using the motor. The device has such advantages as simple structure, convenience for installation, low noise and easy application in shallow water.