Abstract: The durability assessment and damage tolerance assessment of aircraft structure are both based on the crack propagation analysis. The combined analysis method of the durability and damage tolerance in this study is proposed on the basis of the intrinsic relationship between them. The non-probability initial crack size in the damage tolerance design handbook is adopted as the threshold value of crack size. The probability distribution of initial crack size at probability damage tolerance analysis is derived by the probability of the crack size beyond the threshold value and the results of durability analysis. The probability of crack size beyond the threshold value is given by test data. The evaluation system is proved reliable by our examples. The explicit expression of structural safe margin and formulas of the first order second moment method (FOSM) are derived at the damage tolerance analysis in order to avoid the calculation of multiple integrals, which improves the efficiency of computation. Through a comparison of our results with those yield by other method, it is concluded that the proposed method is of reasonable and efficient.