In view of the problems existed in the traditional analysis devices of dissolved gas in transformer oil, such as large size,complicated oil circuit and susceptibility to electromagnetic interference, an analysis system based on optical fiber photoacoustic sensing is designed to detect trace acetylene gas dissolved in transformer oil. In the system, the laser wavelength is optimized through spectral line analysis, and a thermostatically controlled laser driving module is designed. The pump laser and probe light are transmitted into the photoacoustic sensor probe by two single-mode fibers. The photoacoustic signal generated by gas molecules absorbing the pump laser energy is detected by a Fabry-Perot interference cantilever, and then demodulated by a self-designed spectral measurement and signal processing module. Experimental results show that the designed optical fiber photoacoustic sensor system can effectively detect photoacoustic signal of acetylene gas dissolved in transformer oil, with a detection limit of 0.5 μL/L.