The　function　mechanism　of　carbonized　layer　at　the　surface　of　La2O3-Mo　cathode　prepared　by　ion　implanting　method　has　been　discussed　by　using　XPS,　AES.　The　results　show　that　the　carbonized　layer　mainly　acts　as　a　reduction　reagent　to　produce　metallic　lanthanum,　moreover,　it　can　store　the　active　substances　and　carry　them　to　the　surface.　On　the　basis　of　the　research　results,　the　carbonization　technique　has　been　changed.　By　using　the　new　technique,　the　lifetime　of　La2O3-Mo　cathode　has　been　improved　from　14　h　to　1436.5　h.　The　lifetime　has　exceeded　the　minimum　lifetime　for　the　practical　use　(1000　h).