Abstract: This paper presents a set of fundamental equations for reliability analysis of aircraft structures. For a single-critical-point structure, it considers the following factors: the static strength of structure, initial crack, the initiation and propagation and unstability of fatigue crack, the residual strength of structure, the statistical distribution of load, the probability of crack detection, the periods of overhaul, accident damage, the communication of damage among fleets etc. Based on this mathematical model, the influence of the various factors to reliability can be analyzed quant-itively, and the various criteria for fatigue design of aircraft structure can be evaluated from the aspect of reliability.