For the traditional underwater acoustic release device with complex structure, large volume and mass, and difficult dynamic sealing in deep-sea high-pressure environment, a novel piezoelectric actuator for deep-sea release function is proposed. The actuator consists of a piezoelectric composite stator and rotor, and is based on the basic principles of inverse piezoelectric effect and friction transmission, which achieves the separation and release between the stator and rotor through the rotational bending motion coupled by two-phase bending vibration. The proposed actuator adopts a simple and compact structure, is easy to control, reduces the volume and weight of the entire release system, and increases its reliability in deep-sea environments by allowing the friction-driven interface to be directly in contact with seawater, eliminating the need for dynamic seals. First, a three-dimensional solid model of the actuator was established through structural dynamics analysis, and its driving principle was theoretically analyzed. The equation of the elliptical motion trajectory of the stator’s driving mass point was derived. Then, finite element modal simulation and analysis were performed on the piezoelectric composite stator, and the structural parameters of the stator were optimized based on the design requirements of frequency consistency and distance from adjacent interference modes. Finally, the amplitude-frequency characteristics, working mode shape, and driving mass point motion trajectory of the stator were analyzed through finite element harmonic response simulation. This paper proposes a novel deep-sea release piezoelectric actuator, which offers a fresh idea for advancing deep-sea release devices technology.