The　technology　for　detecting　decomposition　products　of　SF6　based　on　carbon　nanotubes　(CNTs)　gas　sensor　can　effectively　diagnose　the　partial　discharge　(PD)　caused　by　insulation　defect　in　GIS.　In　this　study,　the　responses　of　the　CNTs　gas　sensor　to　four　standard　gases,　i.e.　HF,　SO2F2,　SOF2/S2OF10,　and　SO2,　were　measured,　and　an　experimental　system　was　set　up,　which　consists　of　a　GIS　simulation　device,　a　PD　detection　instrument　based　on　pulse　current　method,　and　a　CNTs　gas　sensor.　Then,　the　decomposition　gas　of　SF6　resulting　from　PD　was　measured　by　the　CNTs　gas　sensor,　the　variation　of　conductance　of　the　gas　sensor　with　PD　was　obtained,　and　the　repeatability　of　the　gas　sensor＇s　response　was　analyzed.　The　results　show　that　the　gas　sensor　displays　significant　response　characteristics　in　SO2F2　and　SOF2/S2OF10　gases,　and　it　is　more　sensitive　to　SO2F2.　However,　SO2　and　HF　induce　little　change　in　the　conductance　of　the　sensor.　The　sensor　exhibits　clear　response　to　the　PD　generated　by　point-plane　electrode　model.　Furthermore,　the　conductance　of　the　gas　sensor　increases　gradually　within　the　duration　of　PD,　and　its　response　increases　almost　linearly　with　the　accumulation　of　partial　discharge　energy　until　gets　saturation.　The　gas　sensor　shows　good　repeatability　with　the　difference　between　two　measurements　less　than　0.5%.　The　analyses　of　gas　chromatography　and　infrared　spectroscopy　on　decomposition　products　of　SF6　verify　the　correctness　of　the　proposed　gas　sensor.