Different　grades　of　CVD　diamond　films　were　prepared　by　100　kW　DC　Arc　Plasma　Jet　system.　The　films　were　characterized　using　optical　microscope　(OM),　high-resolution　transmission　electron　microscopy　(HRTEM),　electron　energy-loss　spectroscopy　(EELS),　and　Raman　spectroscopy.　The　results　show　that　dark　feature　mainly　is　inclusions　in　CVD　diamond　films,　the　concentration　are　amorphous　carbon　and　nitrogen.　As　for　transparent　optical　grade　diamond　film,　it　has　very　high　IR　transparency　and　high　thermal　conductivity.　The　appearance　of　dark　feature　degraded　the　quality　of　CVD　diamond　film,　apparently　influencing　IR　transparency　and　thermal　conductivity.　But　even　in　optical　grade　diamond　film,　there　are　very　strong　absorption　features　in　the　7-9　mu　m　region,　this　will　limit　the　practical　applications　of　diamond　films　grown　by　Plasma　Jet　as　IR　windows　for　CO2　lasers.　(c)　2005　Elsevier　B.V.　All　rights　reserved.