Abstract: Tritium is a common radioactive product in nuclear power plants. It is easy to diffuse, penetrate and be easily absorbed by organisms due to its small atomic radius. The tritium produced by fission in pressurized water reactors(PWR) mainly enters the primary circuit through the fuel envelope and serves as an important source of tritium release. Following the Fukushima accident in Japan in 2011, the diffusion of hydrogen isotopes in zirconium alloy cladding has garnered significant attention. The diffusion coefficient, a key parameter for evaluating the risks associated with hydrogen isotope diffusion, is typically measured using gas-driven permeation and electrochemical hydrogen permeation testing methods, as introduced in this study. Moreover, the diffusion mechanism of hydrogen through zirconium alloys under different conditions is discussed in detail. Alloying elements and impurities in zirconium alloys have been reported to provide hydrogen trapping sites. When tin(Sn), iron(Fe), chromium(Cr) and nickel(Ni) coexist, the hydrogen diffusion coefficient decreases. The formation of zirconium hydride and oxides also affects the hydrogen isotope permeation rates differently. Due to lattice distortion and formation of microcracks in zirconium alloy, zirconium hydride results in an increased hydrogen isotope diffusion coefficient. Conversely, the formation of oxides, such as zirconia, on the surface of zirconium alloys can act as hydrogen permeation barriers, preventing further permeation or absorption of hydrogen isotope atoms. A more detailed discussion is presented in the paper. In light of these findings, further exploration of the behavior of hydrogen isotopes in zirconium alloy cladding is essential to enhance the safety of nuclear power plants. To this end, future research endeavors should focus on advanced hydrogen analytical techniques and multiscale modeling approaches. Innovative experimental methodologies could yield more precise data on hydrogen diffusion. Leveraging advanced analytical techniques such as neutron scattering and molecular dynamics simulations could provide deeper insights into the diffusion mechanisms. Integrating multiscale modeling approaches facilitates a comprehensive understanding of hydrogen diffusion in zirconium alloys. Combining atomistic simulations with continuum-scale models enables researchers to elucidate the complex interactions between hydrogen atoms, alloying elements, and microstructural features. Additional studies are necessary to investigate the diffusion of hydrogen isotopes in zirconium alloy in the near future.