Abstract: The fracture cause of a double-screw blot was studied by means of fracture observation, energy spectrum analysis, microstructure examination, hardness and tensile properties testing, and zonal structure rating. The results show that the fracture mode of the bolt is hydrogen embrittlement fracture, and the crack source is at the center of the bolt, where the hardness is much higher than that of other zones. Energy spectrum analysis and microstructure examination show that there is serious segregation of carbon and alloy elements at the source zone, which is the main cause for hydrogen embrittlement cracking at the center of the bolt.