Abstract: By analyzing stochastic of effects on the fatigue crack propagation life, a few models on life reliability of fatigue crack propagation in common use were compared. On the base, a kind of reliability model, so called the reliability model of fatigue crack propagation life corresponding to fracture toughness, was proposed in this paper. The model is based on the distributions of fatigue crack propagation life & fracture toughness, which were generally accepted as Weibull distribution or logarithmic normal distribution. The paradox about the distribution of crack size was avoided, especially for three dimensional cracks, two-directional crack sizes were included in the maximum stress strength factor in front of the crack. It was suitable to the probabilistic damage tolerance evaluation of structures including all kinds of cracks or faults.