A high-precision acetylene (C2H2) detection technology based on a T-type photoacoustic (PA) cell and 2f/1f wavelength modulation spectroscopy is proposed, aiming to address the issues of low sensitivity and weak anti-interference capability in the detection of dissolved C2H2 gas in transformer oil. A distributed feedback (DFB) laser is employed as the light source. Highly selective C2H2 gas detection is achieved by exploiting the characteristic C₂H₂ absorption peak at 1532 nm. The 1f signal generated by the solid-state photoacoustic effect is utilized to eliminate the influence of changes in excitation light power. The system achieves a minimum detection limit (MDL) of 68.5 ppb with an averaging time of 1 s, and a dynamic range covering 1 ppb to 1000 ppm by optimizing the dimensional parameters of the PA cell (including a resonant tube with a diameter of 6 mm and length of 100 mm) and modulation parameters. Experimental results demonstrate that the proposed technology exhibits excellent anti-interference capability and long-term stability, meeting the requirements for online monitoring of dissolved C2H2 in transformer oil. This scheme provides a high-precision and highly reliable detection method for early fault diagnosis in power equipment.