The analysis of accidents indicates that fatigue is the main failure mode in ship structures. Generally, the simplified methods are employed in the engineering because the variable structure details and the different load conditions make this problem very complicated. The general principles of the fatigue life assessment of ship structures are reviewed. A program for calculating fatigue loads, stresses and cumulative damages as well as fatigue life are compiled. As an example, the fatigue life of an oil tanks * structure is analyzed, and the program is proved effective and reasonable.