The performances of a double-beam thin-film interferometric fiber (DBTFIF) microphone based on phase demodulation is studied. The effects of the direct current (DC) subentry, alternating current (AC) subentry and phase difference of three interference signals on the output performances of this DBTFIF microphone are analyzed by simulation. Through the comparison method, the output performances of this DBTFIF microphone based on phase demodulation are studied experimentally as well. The experimental results show that the measurement of acoustic signals with a sensitivity of about 193 mV/Pa at 1 kHz and the frequency response ranging from 200 Hz to 4 kHz with a fluctuation of about ±3 dB can both be achieved. This research can be well used in the fields of acoustic detection, voice recognition, and so on.