The occurrence of discharge due to insulation defects in gas insulated switchgear (GIS) can cause decomposition of SF₆. The low-fluoride sulfide species produced by the decomposition react with trace amounts of H₂O and O₂ in the equipment to produce corrosive substances, which affect the normal operation of the equipment. Thus, it is of great significance to study the decomposition mechanism for the safe operation of GIS. Some decomposition products are transformed in the process of sampling. Hence, it is necessary to realize the in-situ detection of SF₆ decomposition products to study the mechanism of SF₆ decomposition. Femtosecond laser-guided high-voltage discharge technology was proposed to achieve the precise control of the space and time of high-voltage discharge, and the in-situ measurement of SF₆ decomposition products was achieved by using space-resolved spectrum generated by femto second laser-guided high-voltage discharge in our work. In this paper, firstly, the decomposition of SF₆ is not caused by femtosecond laser. Secondly, the precise control of discharge space and time is achieved by using the plasma channel generated by femtosecond laser. Finally, it is found that the decomposition contains a large number of S and F ions and atoms that are directly or indirectly generated by high-energy electron collisions. The research proves that in-situ detection of SF₆ decomposition products can be achieved based on femtosecond laser-guided high-voltage discharge, which provides a new research method for the study of SF₆ decomposition mechanism under high-voltage discharge.