Abstract: Phase spectroscopy of sound pressure reflection coefficient(SPRC) was used to nondestructively characterize the inhomogeneity of plasma sprayed Cr2O3 coatings with the thickness of (50±5) μm. Analyses of amplitude spectroscopy and phase spectroscopy were carried out on the different locations of the coating. Then the velocities measured by amplitude and phase spectroscopy at the locations were obtained. It was found that the velocities measured by phase spectroscopy were different and the change laws between the extremum of phase spectroscopy were distinct. According to the observation of scanning electron microscope(SEM), the differences were attributed to microstructure differences caused by the difference of microstructure caused by the various distributions of porosity, and microcracks. The influence of density on phase spectroscopy was discussed for explaining the differences of the shape of spectroscopy between the variant positions on the same sample, based on the method numerical calculation. Moreover, the results of experiment and numerical calculation showed that ultrasonic phase spectroscopy itself was a good indicator to reveal differences between density and microstructures of coating prepared by the method of plasma spray.