Abstract: The microstructure and chemical composition of S22 alloy steel (S22) were measured by using a optical microscope and a glow discharge spectrometer, respectively. The behavior of deuterium diffusion and permeation in S22 was investigated by using a gas permeation apparatus which was calibrated by a standard leak. The permeability and diffusion coefficient of deuterium at the range of 400-600 ℃ in S22 were measured and calculated. Deuterium permeation in S22 was compared between pure D₂ and 1% D₂ balanced with He. The results show that the diffusion and permeation incubation period of deuterium in S22 increases and the rate of deuterium permeation decreases with the decrease of deuterium pressure. But even at lower deuterium pressure, deuterium penetration in S22 remains. The results can provide theoretical and data support for the necessary tritium permeation protection and safety analysis in the use of S22 in advanced reactors such as high-temperature gas-cooled reactors and fast reactors.