Abstract: The microstructure of SA516Gr70 hot-rolled press vessel steel plate was investigated by optical microscope, scanning electron microscope and transmission electron microscope, and the hydrogen permeation characteristics and hydrogen induced cracking behavior were studied by hydrogen permeation experiment and nondestructive test. The results show that the microstructure of SA516Gr70 press vessel steel plate was banded ferrite and pearlite, and there were a large number of dislocation, a small amount of second phase and some large size composite inclusions. The diffusion hydrogen content in SA516Gr70 press vessel steel plate increased with the increase of hydrogen permeation time, and the limit diffusion hydrogen content was about 0.000 784%. Under the condition of 10 mA·cm-2 electric current density, hydrogen induced cracking would not happen when the diffusion hydrogen content was lower than 0.000 409%. However, when the diffusion hydrogen content was above 0.000 549%, hydrogen induced cracking would happen.