The invention relates to a sandwich type free beam composite bending vibration operating mode unlockable nut, and belongs to the field of fasteners and driving media by means of screw thread pair connection. The sandwich type free beam composite bending vibration operating mode unlockable nut aims at conveniently, fast and flexibly achieving conversion and control of a self locking operating state and an unlocking operating state between screw thread pairs. The sandwich type free beam composite bending vibration operating mode unlockable nut is provided with a nut base body in a free-beam state. A circle of circular groove is formed in middle of the outer circle face of the nut base body in a free-beam state, a piezoelectric telescopic circular ring is embedded in the circular groove of the nut base body in a free-beam state, two side end faces of the piezoelectric telescopic circular ring are respectively connected with those in the circular groove, the piezoelectric telescopic circular ring is composed of a plurality of piezoelectric telescopic pieces, and the driving mode of the piezoelectric telescopic circular ring is a travelling wave vibration excitation operating mode or a stationary wave vibration excitation operating mode. By means of the sandwich type free beam composite bending vibration operating mode unlockable nut, when the piezoelectric telescopic pieces input driving signals, a self locking operating state of the nut base body can be converted into an unlocking operating state, namely, frictional coefficients between the screw thread pairs are greatly reduced, and therefore the self locking operating state between the nut base body and a threaded rod can disappear.