High-Temperature Gas-cooled Reactors (HTGRs) and other Generation IV reactors have demonstrated substantial potential in enhancing nuclear energy efficiency and safety. However, radiation safety continues to be a significant challenge for these reactor. Tritium, a key radioactive isotope of hydrogen, has a small atomic size and exhibits a strong diffusion capability. Therefore, the control of tritium retention and permeation is critical for ensuring the radiation safety of nuclear reactors. This paper begins by discussing the fundamental principles of tritium permeation and provides an in-depth analysis of the mechanisms behind tritium permeation in metallic materials. Further, the study examines the role of oxide layer in inhibiting tritium permeation, considering the influence of oxide layer thickness and quality. By integrating existing theoretical models, the paper also investigates the unique characteristics of tritium permeation in the HTGR operating environment, particularly the combined effects of oxide layer and micro-defects on permeation behavior. In practical applications, it is recommended to adopt a conservative safety analysis approach, where the tritium permeation process is regarded as diffusion-controlled, with diffusion being the rate-limiting step. The square root of pressure dependence should be used for predicting and assessing tritium permeation rates. Future research should focus on experimental validation of tritium permeation behavior under high-temperature and high-pressure conditions, as well as the development of multi-scale models to improve the accuracy of tritium permeation predictions in advanced nuclear energy systems.