Abstract: The corrosion test is conducted to the X65QS anti-corrosion linepipe as per NACE Method A.And the morphology of the fracture of the SCC crack is observed by means of the metallographic microscope and the SEM to find out the cause for the said crack.It is identified via the analysis that there exist Class D inclusions on the fringe of the fracture;hydrogen is acuminated in the inclusion area,forming the stress gathering and the cracking origins;under the co-effect by both hydrogen and the stress,the hydrogen brittle defect is developed in the inclusion defective part,and thus leads to embrittlement of the base metal in the defect part.As a result,the effective stressed area of the specimen is reduced,resulting in fast crack expansion and early-stage fracture of the specimen.