Abstract: A certain 13Cr11Ni2W2MoV bolt is used for the housing coupling positioning bolt, which mainly bears tensile stress and breaks during overhaul. Through macro-observation, fracture analysis and chemical composition analysis, the cause of bolt fracture was analyzed in combination with the working environment and stress conditions when using the bolt. The results show that the gap surface between the bolt and the mating parts are pressed, and corrosion products formed by oxygen, chlorine and other elements in the retention environment occur, and the gap corrosion occurs. Under the action of long-term temperature and load, stress corrosion damage occurs, and eventually overload and break during the disassembly.