A tidal current generating unit, including a turbine, a hub, a generator, a bearing set and a fixed flange. The turbine is connected to the rotor of the generator through the hub, and the rotor is rotatably mounted on the outer circumference of the stator of the generator via the bearing set, and the turbine drives the rotating component to rotate to generate electricity. A density of a blade is much smaller than a density of the seawater, such that the blade has a sufficient buoyancy that offsets the gravity of the rotating component in seawater, and the load of the bearing sets is reduced. The blade is a backswept blade and the hydrodynamic central axis of the blade is inclined from a flange central axis of the blade at a first angle, and the blade is able to automatically change the pitch without relying on an external force.