Abstract: The delayed fracture of a prestressed concrete steel bar occurred in the process of standing. The fracture reasons were analyzed by means of macroscopic observation, chemical composition analysis, hardness test, scanning electron microscopy and energy spectrum analysis, metallographic examination and other methods. The results show that the main reason for the fracture of the steel bar for prestressed concrete was the scarring and micro-cracks on the surface of 30MnSi material. These defects provided conditions for hydrogen-induced delayed fracture.