Abstract Two kinds of multi-layer CVD SiC coatings were prepared on a three-dimensional C/SiC composite. Oxidation behavior of the coating and the composite were studied and the effect of defects in the coating on its oxidation protection property were investigated. Above 1200 °C, thickness of the oxide film formed on the coating was related to oxidation time by the Fick’s first law X( t) 2= Bt, the diffusion rate constant increased with oxidation temperature according to the Arrhenius’ relation ln B=−32 483/ T+1.4048. Morphology of the interface between the CVD SiC and its oxide film was different after oxidation at temperatures from 1200 to 1500 °C. It was interpreted by consideration of the interfacial stress produced by thermal expansion mismatch and the CO gas pressure produced by interfacial reaction.