Abstract: The failure analysis of the bolts was made by macrostructure,chemical composieion,microstructure,fractography and EDS analysis. The results show that the stress corrosion,which is due to the interactions between the stresses and corrosion media ,make the bolts fracture. All of the fastening bolts fracture after used two years,as the bolts was long-term immcrsed in oil which contains the H2S. In addition,inproper material compositions,hardness,and microstructure also result in the fracture of the bolts.