Abstract: The anti-roll torsion bar shaft of a certain type of rail vehicle fractured during the production process, and the fracture occurred in the straightening process after heat treatment. The fracture reason of the torsion bar shaft was analyzed by means of fracture analysis, metallographic examination, mechanical property test and raw material analysis. The results show that the high heating temperature during quenching was the main reason for the brittle fracture of the torsion bar shaft, while the insufficient tempering time, insufficient microstructure transformation and uneliminated stress were another important reasons for the fracture of the torsion bar shaft.