A sulfur hexafluoride (SF 6) degrading device based on thermal plasma, comprising a gas inlet control system which comprises: a carrier gas Ar input line comprising a carrier gas Ar source, a first gas valve and a first mass flow meter; a reaction gas input line comprising a reaction gas source, a second gas valve and a second mass flow meter; a SF 6 gas input line comprising a SF 6 gas source, a third gas valve, a vacuum pump and a third mass flow meter; a thermal plasma generator which comprises: a closed shell comprising a circulating water cooling interlayer and a reaction cavity enclosed by the water cooling interlayer, wherein the reaction cavity is connected to the gas inlet control system, so as to receive a carrier gas Ar, a reaction gas and SF 6 according to a predetermined ratio through three swirlers respectively, wherein the reaction gas is a hydrogen-containing gas or an oxygen-containing gas; three annular electrodes which are respectively a cathode (4.1), an arc strike anode (4.2) and an arcing anode (4.3) and are electrically connected to a direct current power supply to generate a thermal plasma jet flow; a harmless treatment system which is connected to the reaction cavity and is configured to treat solid product and gas product, whereby the harmless treatment system includes: a sulfur powder filtering device communicating with the reaction cavity to filter out sulfur powder in mixed gas from the reaction cavity; an alkali liquid spraying tower communicating with the sulfur powder filtering device and including a mortar pump for cyclically pumping alkali liquid to form a spray; a waste gas detection device communicating with the alkali liquid spraying tower to sample and detect waste gas discharged from the alkali liquid spraying tower. a carrier gas Ar input line comprising a carrier gas Ar source, a first gas valve and a first mass flow meter; a reaction gas input line comprising a reaction gas source, a second gas valve and a second mass flow meter; a SF 6 gas input line comprising a SF 6 gas source, a third gas valve, a vacuum pump and a third mass flow meter; a thermal plasma generator which comprises: a closed shell comprising a circulating water cooling interlayer and a reaction cavity enclosed by the water cooling interlayer, wherein the reaction cavity is connected to the gas inlet control system, so as to receive a carrier gas Ar, a reaction gas and SF 6 according to a predetermined ratio through three swirlers respectively, wherein the reaction gas is a hydrogen-containing gas or an oxygen-containing gas; three annular electrodes which are respectively a cathode (4.1), an arc strike anode (4.2) and an arcing anode (4.3) and are electrically connected to a direct current power supply to generate a thermal plasma jet flow; a harmless treatment system which is connected to the reaction cavity and is configured to treat solid product and gas product, whereby the harmless treatment system includes: a sulfur powder filtering device communicating with the reaction cavity to filter out sulfur powder in mixed gas from the reaction cavity; an alkali liquid spraying tower communicating with the sulfur powder filtering device and including a mortar pump for cyclically pumping alkali liquid to form a spray; a waste gas detection device communicating with the alkali liquid spraying tower to sample and detect waste gas discharged from the alkali liquid spraying tower. a closed shell comprising a circulating water cooling interlayer and a reaction cavity enclosed by the water cooling interlayer, wherein the reaction cavity is connected to the gas inlet control system, so as to receive a carrier gas Ar, a reaction gas and SF 6 according to a predetermined ratio through three swirlers respectively, wherein the reaction gas is a hydrogen-containing gas or an oxygen-containing gas; three annular electrodes which are respectively a cathode (4.1), an arc strike anode (4.2) and an arcing anode (4.3) and are electrically connected to a direct current power supply to generate a thermal plasma jet flow; a harmless treatment system which is connected to the reaction cavity and is configured to treat solid product and gas product, whereby the harmless treatment system includes: a sulfur powder filtering device communicating with the reaction cavity to filter out sulfur powder in mixed gas from the reaction cavity; an alkali liquid spraying tower communicating with the sulfur powder filtering device and including a mortar pump for cyclically pumping alkali liquid to form a spray; a waste gas detection device communicating with the alkali liquid spraying tower to sample and detect waste gas discharged from the alkali liquid spraying tower. a sulfur powder filtering device communicating with the reaction cavity to filter out sulfur powder in mixed gas from the reaction cavity; an alkali liquid spraying tower communicating with the sulfur powder filtering device and including a mortar pump for cyclically pumping alkali liquid to form a spray; a waste gas detection device communicating with the alkali liquid spraying tower to sample and detect waste gas discharged from the alkali liquid spraying tower.