Abstract: In the present paper, the overloading effect on the impact fatigue crack initiation life (IFGIL) of 300M ultra-high strength steel was investigated. The results show that , in a certain limit, the tensile overlonding increases IFCIL. The compressive residual stress induced by overloading is a main mechanism of the effect of overloading on IFCIL, and the varing of material properties which induced by overloading has no significant effect on it. After tensile overloading, the compressive residual strain εR, at the notch root of specimen is related to IFCIL, Ni, by a relation as: NI=N0·exp（λεR）, where No and λ are constants.

Key words: 高强度钢, 疲劳裂纹