Abstract: Cracking and leakage phenomenon occurred at the neck of an austenitic stainless steel flange during operation. Through detecting the material chemical compositions, analyzing the microstructure, observing the cracking fracture surface with scanning electron microscopy and analyzing the corrosion products with X-ray energy dispersive spectrometer, the cracking causes of the flange were analyzed. The results show that the carbon content of the flange material exceeded the standard requirement, and there were a large number of precipitates at the grain boundary due to the heat treatment defects. At the same time, the flange suffered tensile stress and corrosive environment during operation. The above factors together caused the intergranular stress corrosion cracking at the neck of the flange.