The　oxidation　mechanisms　of　iron　particles　and　NiCoCrAlY　particles　during　plasma　spraying　process　and　its　effect　on　the　sprayed　coatings　were　investigated　by　the　in-flight　particles　collection　setup　and　the　gas　shrouding.　The　results　show　that　there　are　two　oxidation　mechanisms　during　in-flight　oxidation:　one　is　the　diffusion　oxidation;　the　other　is　the　convective　oxidation,　which　are　decided　by　the　distance　from　the　spraying　particles　to　the　nozzle.　The　oxidation　content　increases　with　the　increasing　of　the　standoff　distance.　The　shrouded　gas　can　decrease　the　oxidation　content　of　in-flight　particles　and　increase　the　oxidation　resistance　of　NiCoCrAlY　coatings.