Specimens of AISI 321 stainless steel (0Cr18Ni9Ti) of various martensite contents were prepared by the low temperature(-70 degrees C) elongation method. X-ray diffraction (XRD) and transmission electron micrograph (TEM) techniques were used to study the phase transition process and its structure. The relationship between deformation-induced martensite and stress corrosion cracking (SCC) susceptibility of the steel in 42% (boiling) MgCl2 solution was investigated using the constant load SCC test with the normalized threshold values. The results reveal that when the alpha＇-martensite content is less than 5% and also in the range of 15%-24%,the SCC susceptibility of this material decreases with the increase of alpha＇-martensite content.However,when the alpha＇-martensite content is in the rang of 5%-15% and more than 24%, the SCC susceptibility of this material increases with the increase of the alpha＇-martensite content. The SCC fracture surface of the specimens exhibits a stepped fracture surface and transgranular stress corrosion fracture surface morphology.