Abstract: Under the direct observation and record by optical and scanning electrcn microscope,the micro and macro behavior of hydrogen-induced cracking in high temperature charged specimen and weld zone of quenched and tempered Cr-Ni low alloy steel (JIS SNC 631) was evaluated.The mechanism of the initiation and propagation of hydrogen-induced cracking such as the relationship between microcracking and plastic deformation,the relationship between the initiation of HAZ microeracking and sulphideinclusions and the relationship between the mode of fracture and micrcstucture hasbeen further investigated.