Abstract: With the continuous development of the power industry, the safety and stability of transformers are becoming increasingly important. In order to meet the needs of online monitoring of C₂H₂ in transformer oil, a 1532 nm distributed semiconductor laser and a 12 m optical path White cell were selected to develop an online monitoring device for C₂H₂ in transformer oil based on tunable diode laser absorption spectroscopy and wavelength modulation technology. It has achieved functions such as separation of dissolved C₂H₂ in oil, gas detection, and result analysis. The measurement cycle is about 25 minutes, and the testing process involves non-destructive samples. The device detects accurately and quickly, without the need for manual operation, and can provide real-time safety reference opinions for transformers.