Abstract: A Fabry-Perot interferometric fiber-optic infrasound sensor was prepared using a prestressed metal diaphragm, and the low-frequency sound detection test at high altitude was realized based on the aerostat platform. In order to make the fiber-optic infrasound sensor adapt to the change of air pressure during the lifting process of the aerostat, the frequency response characteristics of the sensor under different diameters of the pressure balanced hole were simulated and analyzed, and the relationship between the vibration amplitude of the sensor diaphragm and the diameter of the pressure balanced hole was established. With the guidance of simulation, a fiber-optic infrasound sensor was designed and prepared, and the sensor performance was characterized. The experimental results show that the prepared fiber-optic infrasound sensor has a relatively flat frequency response in the range of 1.5 Hz to 20 Hz with an in-band sensitivity variation of less than 3 dB. The sensitivity of the sensor is 154 mV/Pa@1 Hz, and the obvious infrasound time-frequency domain signal can still be detected at a low of 0.5 Hz. The laboratory-made fiber-optic infrasound sensor head was fixed outside the load chamber of the aerostat, and the low-frequency sound detection test at high altitude was carried out on the Kashgar Plateau. The test results show that the infrasound sensor is sensitive to the sound signal generated by the ground loudspeaker during the whole lift-off stage of the aerostat, and the altitude dependence of the response amplitude of the infrasound sensor was obtained. During the aerostat tethering stage, the characteristic peaks of the infrasound signal generated by the surrounding vehicles were clearly detected many times. The sensor exhibits good environmental adaptability in the process of the lifting and lowering of the aerostat.