Abstract: 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.