SF6　has　been　widely　used　as　an　insulating　and　arc　extinguishing　medium　in　electric　power　equipments.　Detection　of　gas　decomposition　products　is　an　important　means　for　condition　monitoring　and　fault　diagnosis.　Trace　H2O　and　O2　have　a　significant　influence　on　the　species　and　concentrations　of　SF6　decomposition　products.　It　is　important　to　explore　the　influence　mechanism　of　trace　H2O　and　O2　on　SF6　decomposition　products　under　arcing　conditions.　A　series　of　SF6　decomposition　tests　were　carried　out　on　a　40.5kV　SF6　circuit　breaker,　and　a　gas　chromatograph　and　an　electrochemical　sensor　were　used　to　measure　decomposed　components.　First,　the　H2O　content　remained　constant,　and　the　O2　content　and　arcing　energy　changed　in　the　tests.　It　has　been　found　that　the　decomposition　products　of　SF6　are　SOF2,　SO2,　CO,　CO2,　CF4,　C2F6　and　C3F8.　Then,　the　O2　content　remained　constant,　and　the　H2O　content　changed.　The　decomposition　products　are　mainly　SOF2,　SO2,　CO　and　CO2.　Concentrations　of　all　these　decomposition　products　increase　first　and　then　tend　to　be　stable　slowly　over　time,　but　change　differently　with　the　increase　of　H2O　and　O2　contents,　because　H2O　and　O2　play　different　roles　in　the　formation　process　of　each　decomposition　characteristic　components.　©　2019　Institution　of　Engineering　and　Technology.All　right　reserved.