In order to investigate the correlation between irradiation-assisted stress corrosion cracking (IASCC) susceptibility and the magnetic properties of austenitic stainless steel after ion irradiation, the magnetic properties and phase transformation were studied using a vibrating sample magnetometer and synchrotron radiation grazing incidence X-ray diffraction (GIXRD) on an irradiated specimen up to 25 displacements per atom. GIXRD indicated that the body-centered-cubic (BCC) phase was introduced in austenitic stainless steel by ion irradiation. Then, magnetic hysteresis loop analysis was conducted to give a quantitative analysis on the BCC magnetic phase under different irradiation damage and annealing temperature conditions. Based on the fact that postirradiation annealing will eliminate IASCC susceptibility at 550°C for 1 h, a correlation between IASCC susceptibility and magnetic properties was discussed, and a corresponding IASCC evaluation method was developed.