Abstract: The 20MnTiB steel high strength bolt between the steel truss rods of a railway main bridge broke. The causes of bolt fracture were analyzed by means of recheck test, chemical composition analysis, metallographic examination, hardness test, mechanical property test and fracture analysis. The results show that the fracture mode of the bolt was hydrogen induced fracture. The fracture cause was that the content of manganese element in the bolt was too high, which led to the decline of corrosion resistance. The bolt had been in service for a long time in a humid environment, resulting in hydrogen induced fracture.