The　emission　performance　and　mechanism　of　Ba-W　cathode　coated　with　Sc　film　were　studied.　Results　show　that　the　cathode　coated　with　Sc　layer　200　nm　in　thickness　shows　better　performance.　After　heat　treatment　at　1500　C　in　hydrogen,　the　cathode　could　provide　an　emission　current　density　of　21.07}A}/cm^{2　at　1150　C　b.　The　surface　analysis　shows　that　Sc　is　partially　oxidized　during　heat　treatment,　indicating　that　oxidation　improves　performance.　The　experiment　results　are　consistent　with　the　DFT　calculated　results,　where　the　work　function　of　25%　O-25%　Ba　adsorbed　on　the　Sc　surface　is　the　lowest,　which　is　1.4877　eV,　1.8228　eV　and　1.8210　eV　on　the　Sc　(002),　Sc　(100)　and　Sc　(101)　respectively.　©　2023　IEEE.