The decision of latent fault in SF6 gas electrical equipment can be made more timely and accurately through online monitoring of content change of HF, one of SF6 gas decomposition. Tunable diode laser absorption spectroscopic (TDLAS) technology applies the wavelength tunable characteristics of diode lasers to gain the absorption spectroscopy of the selected absorption line of the target gas for the qualitative or quantitative analysis of the target gas. Because of its high sensitivity, high selectivity, short response time and without cross-interference, etc., we can achieve online monitoring and make the detection of HF more direct, accurate and timely through installing the technical equipment in the SF6 electrical equipment monitoring site location. The analysis shows that the TDLAS technology is an effective and reliable method of SF6 online monitoring technique.