According to aeroengine structure integrity program,fracture critical components must be analysed with damage tolerance concept.Due to crack propagation produced by material defects,working defects or fatigue defects can make structure fracture.Therefore,the sufficient damage tolerance should be maintained.It is realized by selecting material correctly,controlling stress level,using the anti fracture structures and reliable inspection.In this paper,the structural reliability concept is applied to studying optimization of materials for maximum reliability under certain stress levels and crack sizes,to investigating variation influences of material strength and stress level on structure reliability.