Abstract: Aiming at the problems of gas pressure fluctuation and background noise in the insulation state detection of gas insulated switchgear (GIS) equipment, a high sensitivity detection method for the insulation state of eco-friendly gases GIS equipment based on photoacoustic spectroscopy technology was proposed. The method used photoacoustic spectroscopy technology to suppress background noise and accurately detect the components of eco-friendly gases. Combined with the maximum correlation minimum redundancy criterion, the insulation state characteristics were optimized to improve the detection pertinence. High sensitivity detection was achieved by building a model with support vector machine. The detection process included photoacoustic signal detection, noise suppression, component concentration determination, feature selection and classification. Experiment results on C₄/CO₂ gas mixtures demonstrated a fitting accuracy of 0.978 for C₄ compoment, and the dynamic response entropy index consistently remaining below 0.1, indicating that the proposed method has excellent detection sensitivity for monitoring the insulation state of eco-friendly gas GIS equipment, capable of accurately capturing the micro molecular movement changes. This provides a reliable basis for the early diagnosis of equipment insulation deterioration.