Single　event　burnout　(SEB)　is　a　common　single　event　effect　(SEE)　occur　in　VDMOSFET,　previous　studies　have　indicated　the　strong　relationship　between　the　device＇s　secondary　breakdown　voltage　and　the　SEB　threshold　voltage.　This　paper　presents　a　grade　doping　buffer　layer　structure　to　improve　the　device＇s　secondary　breakdown　voltage　so　that　enhance　the　resistance　to　SEE.　Through　detailed　simulation,　it　has　been　verified　that　optimized　grade　doping　buffer　layer　can　decrease　the　peak　value　of　the　electric　field,　significantly　improve　the　parasitic　bipolar　turn-on　current　and　the　SEB　threshold　voltage.　Moreover,　compared　to　non-buffer　layer　and　constant　doping　buffer　layer　structure,　the　optimized　grade　doping　buffer　structure　is　a　more　effective　structure　in　SEE　hardened　VDMOSFET.