Abstract: Silicon carbide (SiC) is an important material for shielding nuclear fission products in tri-structural isotropic (TRISO) particles for high-temperature gas-cooled reactors. It has an important influence on the safety performance of TRISO particles. Therefore, it is necessary to study the irradiation behaviors and mechanical properties of the SiC layer of TRISO particles. The irradiation process and nanoindentation process can be described accurately by molecular dynamics simulations. It is helpful to analyze the irradiation behavior and mechanical properties of materials. In this paper, molecular dynamics simulations were used to study the irradiation behavior of equiaxed polycrystalline and long-axis polycrystalline SiC layers obtained from experiments. The calculated theoretical values of the irradiation swelling degree and mechanical properties of the SiC layer are in good agreement with the experimental values. It shows the strong applicability of the potential functions and other simulation system parameters used in this paper. The irradiation behavior of the SiC layer was studied in detail by swelling degree, density, atomic structure type, and point defect evolution. The results show that the grain structure of the SiC layer has no significant effect on its irradiation swelling and amorphization. The amorphization is not directly converted from the crystal structure to the amorphous structure during the irradiation process. The crystal structure is converted into an intermediate state structure and then converted into an amorphous structure. The point defects are mainly C vacancies, Si interstitial atoms, and C antisite atoms in the early stage of irradiation. The difference between the ratio of C point defects and Si point defects gradually disappears after the irradiation dose tends to be saturated. The evolution of amorphization and point defects tends to start nearby the grain boundaries. Irradiation reduces the mechanical properties of SiC layers. It no longer has a significant effect on the mechanical properties of the SiC layer after the irradiation dose tends to be saturated. The changes in the mechanical properties of the SiC layer before and after irradiation were analyzed by load-depth curve and stress & strain. The results show that the decrease in mechanical properties of the SiC layer is closely related to the mechanical behaviors under external force. For example, the bearing capacity and plastic deformation degree decrease, and the stress & strain distribution are disordered. The results provide a quantitative explanation for the irradiation behavior of the SiC layer of TRISO particles and the change of mechanical properties under irradiation. It is helpful to understand the irradiation behavior and relationship between the irradiation behavior and mechanical properties of the SiC layer.