The invention relates to a rotary piezoelectric actuator. The actuator comprises a rotor mechanism, a pre-tightening mechanism, a driving mechanism and a base; the rotor mechanism comprises a rotor and a rotor shaft; the pre-tightening mechanism comprises a hollow pre-tightening frame and a pair of bolts; micro-displacement of the pre-tightening mechanism in the horizontal direction is achieved byadjusting the pressure of the pair of bolts; the driving mechanism comprises a pair of vibrating mechanisms consisting of a pair of mass blocks, vibrating rods, cams and a pair of piezoelectric patches; the vibrating mechanisms are symmetrically connected to the two sides of the outer portion of the hollow pre-tightening frame through the vibration rods correspondingly; the hollow pre-tighteningframe is movably arranged on the base; and the rotor is located on the hollow pre-tightening frame. When the pair of piezoelectric patches receives the input frequency of 152Hz, rotation and swing ofthe pair of vibration rods are excited to drive the cam to swing, the position of the contact point of the cam and the rotor is changed, and positive pressure between the cam and the rotor is changed,so alternative performing of self-locking and sliding of the cam is achieved; the rotor is driven to rotate during the self-locking, the cam is separated from the rotor during the sliding, and the actions are repeated at high frequency, so macroscopic one-way rotation output of the rotor is achieved.