Abstract: Sensitive unit is the key component of the co-vibration vector hydrophones, and its miniaturization helps reduce the overall volume and mass of the hydrophone. Simulation research on the MEMS sensitive unit with stress concentration is conducted in this article. Based on a mass block trapezoidal cantilever beam structure, a single trapezoidal cantilever beam is transformed into a double trapezoidal cantilever beam. Moreover, grooves are etched in the thickness direction near the fixed end of the cantilever beam, further increasing the local stress of the piezoelectric layer of the beam. Sensitivity frequency responses of three different structural cantilever beam models for vector hydrophones are compared by finite element simulation. and performance differences from perspectives of stress distribution on beams are analyzed. It is found that the double trapezoidal cantilever beam structure enhanced hydrophone sensitivity by 7.7 dB than that of single trapezoidal beam. Additionally, increasing thickness of the cantilever beam and etching grooves at its root, will improve the sensitivity and bandwidth for vector hydrophones. The resonant frequency of 80 μm thickness double trapezoidal cantilever beam with a root groove of 40 μm depth and 100 μm width is 1 496.8 Hz, while sensitivity is −210.8 dB@ 630 Hz (ref. 1V/μPa).