The invention aims to provide a buoyancy ball ejection device for an underwater carrier; with a spring for providing a prime power, the buoyancy ball ejection device comprises a buoyancy ball positioning part, a lever conversion part and a buoyancy ball releasing part. A mechanical body provides a connecting platform between the underwater carrier and the ejection device. When the underwater carrier is in normal work, the device can safely keep a non-release state by eagle head hooks; when the underwater carrier completes work and floats onto a water surface, a control system allows a power-loss electromagnet to be electrified to lose magnetism by applying a signal, so that the eagle head hooks are imbalanced in stress so as to generate deflection and lose a contraction effect on a buoyancy ball, then the buoyancy ball is ejected to the water surface having a certain distance from the carrier under the action of the elastic force of the spring, therefore, recycling personnel can successfully recycle the carrier in the premise of keeping a certain safe distance from the carrier. The buoyancy ball ejection device relies on the mechanical method for positioning and releasing, and has the advantages of compact structure, safety, reliability and the like.