Abstract: The corrosion fractured brass nut was investigated by macro-morphology inspection, chemical composition analysis, microstructure analysis, fracture morphology analysis, numerical simulation and energy spectrum analysis. The results show that due to poor material quality and improper manufacture process, the strength and toughness of the brass nut are not sufficient enough. Meanwhile, in the process of manufacture, storage and transportation, brass nut has been in contact with the corrosive medium with high sulfate content. Under the comprehensive action of inner medium pressure, the preload and processing residual stress, the stress corrosion cracking generates along the stress concentration area of the whole brass nut.