Abstract: Tritium is one of the most concerned radionuclides in the field of nuclear fusion and fission. The research on tritium source terms and migration behaviors in nuclear energy systems is an essential subject to ensure the radiation safety of a variety of nuclear facilities. Tritium is capable of diffusing at interstitial sites of materials by interstitial diffusion for its small atomic radius, which makes it possess stronger migration ability than other radionuclides in nuclear systems. Therefore, investigating tritium permeation behavior and elucidating tritium diffusion mechanism in typical in-reactor materials, and in turn developing tritium impeding technology, are of great value for controlling the migration and release of tritium in nuclear facilities. The authors reviewed the tritium permeation model in materials as well as tritium source terms in various typical nuclear reactors. Then the tritium interaction and diffusion mechanism in typical materials are illustrated. Finally, the research progress and development trend of tritium permeation barrier are briefly presented. The research in this paper has important significance for understanding and mastering the tritium diffusion and permeation behavior in typical nuclear reactor materials.