Abstract: Silicon carbide (SiC) materials have many excellent properties, especially high temperature oxidation resistance, radiation resistance and low reaction activity in the presence of water vapor. In the future, it can be used as a new type of fuel cladding to replace zirconium alloy in light water reactor (LWR) and improve the structural integrity and safety of the reactor. However, when SiC materials are oxidized at high temperature after irradiation, the structure and oxidation rate of SiC materials will change, which will affect the properties. At present, it has been confirmed that the oxidation rate of SiC materials will increase after irradiation, but the specific reason is not clear. Therefore, the relationship between the lattice damage and the accelerated oxidation rate of SiC materials with different crystal forms after irradiation was studied. The experimental materials are 6H-SiC single wafer and SiC poly crystalline wafer, and they were irradiated by 5 MeV and fluence of 5×1014 cm-2 Xe20+ ions at room temperature. After that, the irradiated samples were oxidized by dry air at 1 300 ℃ for 1 h. The irradiated and unirradiated areas of SiC with different crystal forms before and after oxidation were compared by means of X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The results show that irradiation destroys the lattice order and causes lattice damage. These damages promote the formation of a variety of SiO2 groups in the process of oxidation. Due to the difference of thermal expansion coefficient between SiO2 oxide layer and SiC matrix and recrystallization, SiC material produces internal stress. It leads to the rupture of SiO2 oxide film on the surface and accelerates the oxidation. In the process of oxidation, partial C atoms in SiC are replaced by O atoms, which will form gases such as CO, CH2 and so on. The gases spills out of SiC, and the pores formed on the surface also accelerate the oxidation. The cross-sectional TEM images show that the thickness of the oxide layer formed is about 140 nm. However, the thickness of the oxide layer is not uniform and the interface between the oxide layer and SiC is wavy in the local area. This shows that the defects formed after irradiation and oxidation provide an oxygen diffusion channel and promote the oxidation in the area near the stacking fault, which is an important reason for accelerating the oxidation rate.