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[Objectives] The service life of a modern LNG carrier is normally no less than 40 years,which makes the hull bear much more structural alternating cyclic stress than other types of merchant cargo ship with an average service life of 20 to 25 years. There fore,it is necessary to perform fatigue strength analysis of LNG carriers.[Methods] In this paper,The study of the fatigue strength of large membrane LNG carriers such as a 170 000 m3 LNG is conducted adopting the spectral fatigue analysis method. Based on the wave environment of the North Atlantic Ocean and a 40-year designed fatigue life goal with full loading departure and ballast departure loading conditions,with optimization in some areas,the cumulative fatigue damage and fatigue life are calculated according to spectral analysis.[Results] The results show that,the optimized fatigue strength of the ship structure meets design requirements.[Conclusions] This paper proposes the design optimization of critical regions and corresponding hotspots,and puts forward recommendations for quality control during construction and operation to improve structural fatigue performance,thereby providing references and support for the study of large membrane LNG carrier fatigue strength and related hull quality control in the construction and operation stages.