In order to understand the change of mechanical properties of high strength fastener steel under different trace hydrogen contents, SCM435 steel, which is often used to produce highstrength fasteners, was used as research object. The slow tensile strainstress curves under different hydrogen charging conditions of cathodes and corrosion were investigated. The slow tensile fracture morphology was observed by scanning electron microscope (SEM). In addition, the hydrogen evolution curves of slow tensile samples were measured by thermal desorption spectroscopy (TDS), and the measured hydrogen content was compared. The results showed that the hydrogen content in the steel increased gradually with the decrease of the hydrogen charging potential of the cathode after quenching and tempering SCM435 into grade 10.9. The hydrogen in the steel was dominated by the low temperature hydrogen. Hydrogen significantly reduced the ductility of the steel. Moreover, the fracture characteristics of slow tensile also changed from dimple to intergranular fracture, and the brittle fracture occurred.