Abstract: The materials investigated in this experiment were domestic pipeline steel that have same grade. The susceptibility of four specimens to HIC were investigated according to National Association of Corrosion Engineers (NACE) TM0284-2003.Then observe the microstructures of the section using optical microscope and scanning electronic microscope (SEM). The effect of microstructures on the susceptibility to HIC of the tensile samples was evaluated referring to the primitive mechanical properties of the specimens. The results indicate that samples possessed large laths structure and that with inhomogeneous structure showed high susceptibility to HIC. But the cracking paths and the mechanisms are different. At the same time, we also find that the susceptibility of this grade of pipeline steel to HIC is irrelative with the grain size.