Methane and acetylene are the most important characteristic gases when the transformer breaks down. In order to meet the demand for detecting the concentration of the trace CH4 and C2H2 dissolved in the transformer, the laser photoacoustic spectroscopy gas detection technology was adopted. By analyzing the near-infrared absorption spectrum of CH4 and C2H2 gas, the appropriate laser light source was selected and the laser modulation parameters were determined. A set of photoacoustic spectroscopy trace CH4 and C2H2 gas detection system with dual laser light source and a non-resonant photoacoustic cell were designed, and the detection sensitivity and low concentration detection error of the system for CH4 and C2H2 gas was obtained. The result shows that CH4 and C2H2 have good response linearity in the volume fraction range of 0~1000×10-6 and 0~500×10-6, respectively, and the responsivities are 5.8969μV and 16.1831μV per 10-6 volume fraction, respectively. The system is tested for repeatability and accuracy using low-content CH4/C2H2 mixed gas. The maximum absolute error of detection is 0.30×10-6 when the CH4 volume fraction is 3.00×10-6, and the maximum absolute error of detection is 0.20×10-6 when the C2H2 volume fraction of 0.50×10-6. The research results meet the technical index requirements of measurement error and achieve high-sensitivity detection of trace CH4 and C2H2.