In order to further improve the detection sensitivity of multi-component trace gases, an acoustic resonant cavity and an interferometric fiber optic acoustic wave sensor were used to enhance the excitation and detection of the Photoacoustic (PA) signal. A fiber optic PA sensing system was designed to achieve high-sensitivity detection of C₂H₂ and CH₄ gases. To increase the amplitude of the PA response and reduce the cross-interference of other gases, two DFB lasers with center wavelengths of 1 532.83 nm and 1 650.96 nm were selected as the excitation light sources for C₂H₂ and CH₄. Through the digital-to-analog converter, the working parameters such as modulation frequency, bias current and modulation depth of the two DFB lasers were controlled by FPGA. Two near-infrared lasers with different wavelengths were coupled through a wavelength division multiplexer and then incident into the PA cell, achieving dual-component gas excitation of C₂H₂ and CH₄. To further improve the detection limit of gases, a multi-pass device composed of two coaxial concave mirrors combined with a resonant PA cell formed a multi-pass resonant PA cell. The excitation light was reflected multiple times in the multi-pass resonant PA cell, which increased the interaction length between the target gas and light, increasing the effective power of the excitation light. The Micro-electro-mechanical Systems (MEMS) cantilever in the fiber optic acoustic sensor was used as the acoustic sensitive element, and a fiber optic Fabry-Perot (F-P) interference structure was designed to convert the deflection displacement of the cantilever into the change of the F-P cavity length. A superluminescent diode with a central wavelength of 1 550 nm was used as the detection light source. The emitted broadband light entered the acoustic wave sensor after passing through the optical fiber circulator. The F-P interference spectrum containing PA information was detected by the miniature optical fiber spectrum module. The signal processing circuit performed high-speed acquisition and real-time processing of the F-P interference spectrum. By using high-resolution spectral demodulation technology, ultra-high sensitivity PA signal detection based on fiber optic F-P sensor was realized. In order to obtain the highest detection sensitivity, the relationship between the PA response and the modulation parameter was measured by adjusting the modulation current of two DFB lasers. The PA response was measured under different currents, and the system obtained the best detection performance when the modulation currents of the C₂H₂ laser and the CH₄ laser were set to 8.5 mA and 4 mA, respectively. The frequency response of the system was tested to obtain the best PA signal amplitude. In the range of 500 Hz to 1 250 Hz, the modulation frequencies of the two DFB lasers were adjusted, and the resonance peak appeared at 1 660 Hz in the two frequency response curves. The linearity of the sensing system was evaluated. The gas mixtures of C₂H₂/N₂ and CH₄/N₂ with different concentrations were flushed into the PA cell, and the PA response of the system to C₂H₂ and CH₄ was analyzed. In the concentration range of 0 ppm to 100 ppm, there was a good linear relationship between the excitation PA signal amplitude and the concentration of the two mixed gases, and the linear responsivity of the system to C₂H₂/N₂ and CH₄/N₂ were 7.39 pm/ppm and 5.67 pm/ppm, respectively. Pure N₂ gas was pumped into the PA cell to test the noise level of the system and evaluate the stability of the sensor. Two sets of noise data were tested repeatedly, the deviation (1σ) were 0.364 pm and 0.365 pm, and the average value was 0.36 pm. Based on sensitivities of 7.39 pm/ppm and 5.67 pm/ppm for C₂H₂ and CH₄ gases, detection limits of 48.7 ppb and 63.4 ppb were obtained, respectively. The detection sensitivity and stability of the system were evaluated by Allan-Werle deviation analysis. When white noise dominates, the Allan-Werle variance value decreased as the averaging time increased. With an average time of 400 s, the results of Allan-Werle analysis of variance showed that the detection limits of the system for C₂H₂ and CH₄ gases reached 2 ppb and 3 ppb, respectively. The Normalized Noise Equivalent Absorption (NNEA) coefficient normalized the absorption line intensity and the effective power of the excitation light. The output powers of C₂H₂ and CH₄ lasers were 14.7 mW and 21.9 mW respectively. Therefore, the calculated NNEA is 8×10^-10 cm^-1 WHz^-1/2. The designed optical fiber PA sensing system realized the high sensitivity detection of C₂H₂ and CH₄ gas.