A MEMS acoustic vector sensor with high directivity was designed. The structure employed SOG technique to increase fluid gap and decrease vibration damping, and the ANSYS software was used to analyze the influence of the fluid gap on the directivity. The high directivity of the structure has been verified. The result of simulating calculation showed that when the fluid gap changed from 5 μm to 30 μm, the amplitude increased to about 30 times, and the phase difference increased by 126° maximally; when the variable quantity of the incident angle was 80°, the phase difference increased to 40°, and the directivity and the sensitivity were enhanced evidently. The design was conducive to the development of the acoustic vector sensor.