In　this　paper,　accelerated　irradiation　test　of　4.5kV　IGBT　(Insulated　Gate　Bipolar　Transistor)　was　carried　out　by　an　atmospheric　neutron　irradiation　instrument　based　on　China　Spallation　Neutron　Source　(CSNS).　The　experiment　confirmed　atmospheric　neutron　irradiation　caused　single-event　failure　of　the　IGBTs.　The　IGBT　failure　occurred　as　the　collector　voltage　increased　to　a　critical　value.　The　failure　mechanism　of　4.5kV　IGBT　under　neutron　irradiation　was　investigated　by　Sentaurus　TCAD　simulation.　The　simulation　results　indicate　that　with　the　increase　of　applied　collector　voltage,　IGBT　has　a　propensity　to　destruct,　and　the　single-event　burnout　(SEB)　occurs　when　a　certain　threshold　is　exceeded.　The　change　of　electric　field　distribution　reveals　that　the　root　causes　of　SEB　in　IGBT　are　the　avalanche　multiplication　effect　and　parasitic　thyristor　latch-up.　In　addition,　the　influence　of　different　structural　parameters　on　the　burnout　threshold　is　discussed,　which　provides　ideas　for　the　anti-radiation　reinforcement　of　IGBT.