According to the working principle of piezoelectric microphones, the equivalent lumped element acoustic electric model of a piezoelectric sensor was established, and the influence of the vent structure on the sensitivity of the piezoelectric microphone was analyzed. Through finite element modeling, the effects of the vent's geometrical sizes on the low frequency output of the piezoelectric microphone were studied. The locations of ventilating holes at different positions of the silicon base have no effect on the low frequency output of the microphone. When the cross sectional area of the venting holes keeps constant, the longer the vents length, the higher the low frequency response. When the length of the vent keeps constant, the smaller the cross-sectional area, the better the low-frequency response. When the cross-sectional area ratio of the vent holes is 2, if the same low-frequency displacement output is to be achieved, the length ratio should be 4.