A micro-fiber-optic acoustic sensor based on the high-quality-factor (high-Q) resonance effect that uses a Fabry-Pérot etalon (FPE) is presented in this study. The device has been demonstrated experimentally to be a high-sensitivity acoustic sensor with a large dynamic range over a wide frequency band. Optical contact technology was used to improve the robustness of the FPE, which consists of two parallel lenses with high reflectivity exceeding 99%. An acoustic signal detection system based on phase modulation spectrum technology was also constructed. A stable and high-Q value of 106 was measured for the FPE. As a result, high sensitivity of 177.6 mV/Pa was achieved. Because of the change in the refractive index of the air when it is modulated by the acoustic waves, a frequency response of 20 Hz-70 kHz with flatness of ±2 dB was obtained and a large dynamic range of 115.3 dB was measured simultaneously. The excellent performance of the device will be beneficial for optical acoustic sensing.