Fiber optic acoustic sensors are widely used in industry, medical and other fields. In order to improve the performance of fiberoptic Fabry-Perot acoustic sensors, a L-shaped spoke structure Fabry-Perot sensing diaphragm is proposed in this work. The thickness of the diaphragm is 15 μm, the width of the beam is 0. 5 mm, and the radius of the center diaphragm is 1 mm. The diaphragm is etched on 304 stainless steel by laser processing technology. In the experiment, the sensitivity of the sensor at 1 000 Hz was investigated, and the sensor was applied to a photoacoustic spectroscopic gas detection system with a photoacoustic cell resonance frequency of 1 600 Hz, and measurement of acetylene (C2H2 ) gas concentration from 50~ 100×10 -6 was achieved. The experimental results indicate that the sound pressure sensitivity of the sensor is 25. 4 nm/ Pa at 1 000 Hz, the minimum detectable sound pressure (MDP) achievable by the sensor is 38. 2 μPa / Hz 1/ 2@ 1 kHz, and the acoustic pressure signal-to-noise ratio is 76. 8 dB. The peak of the second harmonic signal of the photoacoustic spectroscopy obtained from the experiment shows a good linear relationship with the acetylene concentration, and the response of the acetylene concentration is 1. 8 pm/ 10 -6 . The sensor has a wide range of applications in the field of single-frequency acoustic signal detection, such as photoacoustic spectroscopy.