<p>The photoacoustic spectroscopy apparatus based on an external cavity quantum cascade laser was employed to simultaneously detect four SF₆ decomposition by-products, i.e., SO₂F₂, SOF₂, CF₄, and SO₂ for the application in diagnostics of the SF₆ insulation equipment widely used in high-voltage transmission lines. The influence of background gases SF₆ and N₂ with the He addition in different ratios on the SOF₂ photoacoustic signal was investigated, with the pure SF₆ showing the most pronounced enhancement effect on the photoacoustic signal of the target analyte. The limit of detection of SOF₂ in pure SF₆ was estimated by comparing the limits of detection of SOF₂, CF₄, and SO₂ in the 95% SF₆/5% He combination and pure SF₆. The estimated detection limits for SO₂F₂, SOF₂, CF₄, and SO₂ were 635.4 ppb, 24.0 ppb, 10.3 ppb, and 97.8 ppb, respectively. Finally, the concentration of each decomposition component in the gas mixture of SO₂F₂, SOF₂, CF₄, and SO₂ in the 95% SF₆/5% He background gas was quantified by multiple linear regression.</p>