In order to evaluate the time-dependent fatigue fracture probability of welded joints in ship hulls, a reliability approach was developed.Firstly, on the S-N diagrams, the probability density of stress range, considering yield stress and weld residual stress, was determined in the lognormal format.Secondly, the relation of stress range and the number of stress variations was examined, based on the full scale model tests. It was found out that the distribution of the stress range which is exceeded once out of total number of stress variations may be fitted into the lognormal distribution.Finally, the S-N relation was combined with the relation between stress range and frequency, using the effective stress technique based on the modified Miner's law and the reliability approach. Then the time-dependent safety index and fatigue fracture probability were caculated.