SF₆ gas may be ionized or decomposed into a variety of gases when discharge or overheat occurs. These decomposed gases can affect the insulation of electric power equipment. However, all of the existing infrared gas detection means can not measure the decomposed SF₆ gas on line in situ. According to the practical needs, an infrared spectrometer system based on the principle of a grating is designed. The system can measure the components and contents of the decomposed SF₆ gas in real time and can operate on line when the electric equipment is in the running state. The measured data provide convincing gist for the analysis of the performance and safety of the electric equipment.