The　Ta2O5　isolation　medium　thin　film　was　prepared　with　the　anodic　oxidation　process.　The　morphology　and　composite　of　Ta2O5　film　were　characterized　by　scanning　electron　microscope　(SEM),　X-ray　diffractions　(XRD)　and　pectroscope　(EDS),　respectively.　The　results　indicated　Ta2O5　film　was　amorphous　and　had　better　surface.　The　electrical　breakdown　field　intensity　test　system　studied　insulated　performance　of　Ta-Ta2O5-Al　composite　films　(MIM　structure)　in　the　FED　component,　indicated　that　the　composite　films　had　higher　breakdown　field　intensity,　which　was　2.3　MV/cm.　To　analyze　Ta-Ta2O5-Al　composite　films　breakover　mechanism,　The　schottky　effect,　F-N　Effect　were　respectively　regarded　as　the　main　mechanism.