Abstract: The stress corrosion cracking (SCC) behavior of AL-6XN alloy in supercritical water with 550-650℃ and 25 MPa was studied by slow strain rate test (SSRT). The facture morphology and gauge surface crack of the specimen were observed by scanning electron microscopy (SEM). In 550℃ test condition, the material presents transgranular cracking. Many uniform distributed cracks appear on the gauge surface, and fan-shaped river patterns appear at the corners on the fracture surface. In 650℃ test condition, the material displays intergranular cracking. The fracture surface reveals typical rock candy pattern, and much fewer cracks appear at the fracture end on the gauge surface. Proton irradiation at 550℃ has little effect on the mechanical property of AL-6XN, but induces more fan-shaped patterns (cracking origins) and wider slipping steps. AL-6XN alloy presents severe SCC sensitivity in supercritical water, which is enhanced by higher temperature and proton irradiation.