Abstract: Based on Paris formula,a fatigue crack growth probability model was established in consideration of the influence of stress ratio on fatigue crack growth rate and the dispersion of fatigue crack growth.The parameters of this probability model were estimated by using the principle of no-linear function linearization.Through this probability model and surfaces,the regulations of the effect of stress ratio on fatigue crack growth can be mastered and the probability fatigue crack growth rate curves at any stress ratios can be obtained.Availability and feasibility are indicated by an analysis of the 30CrMnSiNi2A steel test data.