La2O3　and　Y2O3　co-doped　Mo　secondary　emitters　were　prepared　by　three　kinds　of　doping　method　combined　with　high　temperature　plasma　sintering.　The　secondary　electron　emission　property　and　microstructure　of　the　cathodes　were　studied.　It　showed　that　the　cathode　prepared　by　liquid-liquid　doping　method　exhibited　the　best　emission　property　among　all　the　samples　prepared　by　liquid-solid　doping,　solid-solid　doping　and　liquid-liquid　doping　methods　due　to　a　uniform　distribution　of　different　substances.　RE2O3　existed　uniformly　at　the　grain　boundaries　and　diffused　to　the　cathode　surface　during　a　cathode　activation　period.　A　surface　layer　of　RE2O3　formed　after　activation　played　an　important　role　in　the　emission.　The　secondary　emission　yield　of　La2O3　and　Y2O3　co-doped　Mo　prepared　by　liquid-liquid　doping　method　was　4.34.