A kind of novel fiber cantilever vibration sensor with the structure of single mode-multimode-gap-single mode (SMGS) fiber is proposed based on the effect of multimode interference. The beam propagation method (BPM) is adopted to simulate the light propagation in the fibers. The finite element model of the cantilever is established in order to analyze the vibration characteristics of the optic-fiber cantilever, and the optimal design of this kind of fiber vibration sensors is conducted in theory. In the experiments, the fiber cantilevers with the length of 22 mm are fabricated by four different lengths of multimode fibers. The characteristics of cantilevers vibration with different lengths of multimode fibers are analyzed in details. The experimental results agree well with the theoretical simulation results. It shows that the proposed SMGS sensor has the maximum sensitivity of 4 mV/mPa at the frequency point of 130 kHz and the linear correlation coefficient of 0.9962. The experimental results indicate that this kind of sensor has a linear response and good repeatability within given sound pressure level. The proposed sensor maintains the advantages of easy-preparation, low-cost and high-sensitivity, which is expected to be applied to the field of the remote vibration sensing of some special resonance frequency points.