In fission reactors, the application of coatings to cladding tube is an effective strategy to prevent tritium leakage. In this study, Fe–Al/Al2O3 tritium permeation barrier coatings were prepared using a low-temperature embedding process. The coatings were irradiated with 6 MeV Au ions to a dose of 30 dpa. The effects of irradiation on the microstructure, deuterium permeation resistance, deuterium release behavior, and mechanical properties of the coatings were investigated using TEM, gas-driven permeation tests, TDS, and nanoindentation techniques. The results demonstrate that changes in tritium permeation resistance after irradiation are associated with defects such as cracks, voids, and delamination observed in the coatings. These defects facilitate tritium diffusion within the coatings, leading to a decrease in permeation resistance. Conversely, they can act as “tritium traps”, enhancing tritium retention capacity. Compared to the unirradiated state, the PRF of the Fe–Al/Al2O3 coatings decreased by approximately fivefold after irradiation, however, the PRF value remained at 29, indicating that the coatings still exhibit good deuterium permeation resistance.