Acoustic sensor and photoacoustic cell are key components of laser-based photoacoustic spectroscopy. In this paper, we proposed an air-backed mandrel fiber optic microphone with a resonant photoacoustic tube, combining the technologies of fiber Michelson interferometer, phase generated carrier demodulation, and longitudinal resonant photoacoustic cell. In the microphone, we fabricated a sensing arm by wrapping a 10-meter ultra-thin single-mode fiber on a copper capillary tube that was also utilized as the resonant tube of the photoacoustic cell. Besides, a 5-cm reference arm has been isolated from sound and vibration. Furthermore, the resonant frequency of the microphone was designed to be slightly lower than the first-order longitudinal resonant frequency of the photoacoustic cell to achieve quasi-double resonance as the resonant frequency of the microphone was stable. The experimental results show that the minimum resolution is 0.69 μPa/Hz ^1/2 at the resonant frequency of 1443 Hz, and the linearity of acoustic pressure and voltage response is 99.98% (5 mPa-3 Pa) with a dynamic range of 112.52 dB at 1 kHz. In conclusion, the microphone can be applied for trace gas detection in high-temperature, explosive, or high-electromagnetic-interference environments.