Abstract: The fracture reasons of a tie bar had been analyzed by means of chemical compositions analysis, fracture analysis, macroscopic examination, metallographic examination and mechanical properties test. The results show that the delayed fracture of the tie bar mainly resulted from the combination of thermal quenching residual stress and hydrogen in the steel, and the extra stress after slow loading caused hydrogen embrittlement when loading test. Severe banded segregation increased the additional structural stress as well. Finally corresponding methods and suggestions were put forward.