Abstract: The chemical composition,mechanical properties,metallurgical,fracture appearance as well as fracture spectrum of an 1Cr5Mo elbow was experimentally analyzed. An finite element method was used to investigate the stress distribution of the elbow,in order to analyze the causes for its fracture. The results showed that because the elbow was of higher carbon content and of worse plasticity.So the cracking initiated in the inside wall of the tube under the corrosion of the medium,and gradually spreaded in the high stress area,finally caused the through shake,which was a typical stress corrosion cracking.