Abstract: Using plasma spray technology iron particles were sprayed with different spray distances to prepare coatings.The surface and cross-setcion morphology of iron particles and coatings were investigated by scanning electron microscopy (SEM).The oxygen contents of particles and coatings were determined by nitrogen-oxygen determinator.The results show that there were two oxidation mechanisms during in-flight oxidation.One was diffusion oxidation,and the other was convective oxidation.The oxidation of iron particles was mainly convective as the spraying distance was less than 50 mm.After the distance was more than 50 mm,it would be mainly diffusion oxidation.The iron particles were oxidized after the coating formed.The oxidation degree of iron particles during flight was nearly the same as that of after coating formation.