An infrared radiation model for high temperature ceramics under aerodynamic heating condition was developed by analyzing the relationship between the internal thermal radiation. the temperature field of heat transfer, as well as the reflection and refraction at surface. The control volume method combined with the Monte Carlo method and spectral model were used to simulate the radiation heat transfer in the ceramics and outgoing process. The medium effect factor was introduced to analyze the infrared radiation mechanism of the material and the effects of aerodynamic heating on the infrared characteristics. The results show that the coupling of spectral selectivity of thermal radiation inside the high temperature ceramics of the temperature field results in the dependence of material infrared emissivity on the heat flux of aerodynamic heating. The high temperature ceramics absorbs radiation in the ultraviolet, mid-infrared, and the far infrared intensively while absorbs radiation in visible spectra and near infrared weakly. So, the effective region inside the material, where the thermal radiation of medium can contribute to the infrared emission of the material surface, enlarges will the increase of aerodynamic heating, but the infrared emissivity of material decreases.