Abstract: Examinations and tests of some fractured maraging(c) 350 torsional rods were performed by means of SEM,electronic energy spectrum,ICP spectrum and so on. The result of causal analysis showed that the mechanism of the fracture which caused by the stress far below the ultimate strength was mainly related to the hydrogen embrittlement of the material,and intergranular corrosion,which had took place on the surface of the fractured rods during the long-term service process,was the inducement of the hydrogen embrittlement. The characteristic phenomena of the fracture were described.