In this paper, a method is proposed to quantitatively estimate the decrease in threshold stress intensity factor (SIF) range due to high maximum SIF, that is observed for some materials in constant maximum SIF fatigue crack growth tests. The parameters for the simulation were inversely determined from the experimental data of carbon steel, Al and Ti alloys with the aid of genetic algorithm. The set of candidate parameters named as a “generation” were repeatedly generated and evaluated until the experimental data were reproduced by the simulation. A very interesting fact was that though the test conditions for these three materials were different, the obtained simulation parameters seemed to be independent of material. Finally, the proposed method was validated by comparing predictions with experimentally determined values of the decrease in threshold on an embrittled carbon steel.