The invention provides a buoyancy-type optical fiber switch, and the switch comprises a pedestal, a buoyancy key, a transmitting optical fiber, and a receiving optical fiber. A side surface of the pedestal is provided with a balance weight hole, and the central part of the pedestal is provided with a central hole slot. The periphery of the central hole slot is provided with bulged points. The buoyancy key is provided with a through hole, and the bottom is provided with a perforation. The transmitting optical fiber and the receiving optical fiber are inserted to the front of the central hole slot from the holes at two sides. The lower end of the buoyancy key is inserted from the central hole slot of the pedestal, and the bottom is fixed with the perforation through a connection pin, therebyforming a key-type optical fiber switch. Aiming at the transmission characteristics of an optical fiber in liquid, the two optical fibers are placed in a reasonably designed light machine composite system, and the buoyancy key is designed, and is enabled to automatically generate a restoring force through the buoyancy of the liquid, so there is no need of restoring devices, such as a spring or amagnetic device. Therefore, the additional configuration of a fiber collimator is saved, and the cost is reduced. The switch is suitable to be used in the liquid.