Abstract: By taking two typical laboratory specimens of A508 steel, namely single-sided notch bending （SENB） and compact tensile （CT）, as the research objects, on the basis of the similarity principle of mass transfer and heat transfer processes, the coupling analysis of hydrogen diffusion and stress field was conducted by the finite element software ABAQUS, and the hydrogen mass fraction distribution, and the hydrogen-induced stress distribution and variation in the crack tip area under different restraint conditions （the ratio of crack length a to specimen width W, a/W was 0.1, 0.3, 0.5, 0.7） were studied by simulation. The results show that with the extension of diffusion time, the hydrogen mass fraction at the crack tip of both the SENB specimen and the CT specimen increased first and then tended to stabilize. In the early stage of hydrogen diffusion, the hydrogen mass fraction at the crack tip of the CT specimen changed slowly, and the stable hydrogen mass fraction at the crack tip of the CT specimen was lower under the same constraint condition. With the increase of a/W, the hydrogen mass fraction at the crack tip decreased. During hydrogen diffusion, the hydrogen-induced stress at the crack tip of the SENB specimen initially increased rapidly, then decreased, and subsequently increased again before stabilizing. Under a/W=0.1, the hydrogen-induced stress at the crack tip of the CT specimen initially increased rapidly, then decreased, and finally was stabilized. Under a/W≥0.3, the hydrogen-induced stress at the crack tip initially increased rapidly, followed by a plateau, then continued to increase, and eventually was stabilized. After hydrogen diffusion was complete, the hydrogen-induced stress in the SENB specimen was concentrated at the crack tip under a/W=0.1. As the constraint increased, the hydrogen-induced stress distribution became more uniform. The hydrogen-induced stress of the CT specimen was not concentrated at the crack tip and did not tend to be uniform under a/W=0.1, while concentrated at the crack tip under a/W≥3.