The　effect　on　field　emission　properties　of　carbon　nanotube　(CNT)　oxidized　by　HNO3　and　HNO3-H2SO4　were　investigated　by　TEM,　Raman　and　XPS.　The　results　showed　that　the　impurity　of　catalyzer　and　amorphous　carbon　had　been　eliminated　by　the　oxidation　of　HNO3　or　HNO3-H2SO4.　For　the　effect　of　oxidization　and　dehydration　of　H2SO4,　the　higher　disorder　degree　and　more　disfigurement　density　were　obtained　of　carbon　nanotubes　treated　by　HNO3-H2SO4　than　that　of　those　treated　by　HNO3,　with　the　oxidized　groups　such　as　C-OH,　CO　and　COOH　in　existence　of　surface.　The　turn-on　field　of　carbon　nanotubes　treated　by　HNO3-H2SO4　is　1.1V/μm,　which　is　lower　than　that　of　those　treated　by　HNO3　as　1.7V/μm.　The　corresponding　emission　current　density　is　1.8　and　4.2mA/cm2　for　carbon　nanotubes　treated　by　HNO3　and　HNO3-H2SO4,　respectively,　while　the　applied　field　increased　to　3.0V/μm.