Fatigue damage is one of the main causes responsible for the destruction of ship structures. The traditional methods of the fatigue strength check are based on S-N curves and Miner linear cumulative damage rules. But different fatigue lives of the same node are obtained, because the disadvantages of S-N curves could not be avoided, such as neglect of initial objection of material. The method of fracture mechanics to assess the fatigue life of ship structures has become a trend now. According to the relevant fracture mechanics theory, this paper brings forward a set of methods on the fatigue life of ship structures under random sea state. This method takes into account the non-linear effect of stress distributed along the crack surface, and the stress intensity factor is calculated through the weight function method. The crack extension is calculated in each cycle of stress according to the stress response history of ship in actual sea state so as to attain the fatigue crack propagation life of ship structures in the random load.

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