To decrease the interdiffusion, CrON interlayer as a diffusion barrier was introduced into the interface of NiCrAlY overlayer and DSM11 substrate. The microstructure and effect of the diffusion barrier were investigated. It was found that the as-deposited CrON diffusion barrier was comprised of Cr2O3 and CrN. During thermal treatment (including vacuum heat treatment and thermal exposure), the diffusion barrier was first transformed to Al2O3 and Cr2N, then to Al2O3 dominant interlayer, and porous mixed-oxides including TiO2 and NiCr2O4 spinels were detected in the interdiffusion zone between the diffusion barrier and the substrate. The presence of α- Al2O3 in the diffusion barrier was the main reason for suppressing the interdiffusion. The interfacial reaction mechanism in the diffusion barrier was discussed by elemental diffusion and chemical reaction thermodynamics.