Abstract:  Based on the offshore spectrum fatigue theory, this paper is to calculate the fatigue strength and life predication of truss spar platforms. By means of the classical wave spectrum theory and the engineering fatigue theory, a software tool is developed for the spectrum fatigue analysis of structures. Meanwhile, based on the Goodman theory, the effect of mean stresses on fatigue limit is evaluated. The developed software is linked with a finite element analysis tool for offshore structures. Then, the chain work of finite element modeling, hydrodynamic load calculation and mapping to structural models, finite element strength analysis, and fatigue computation is automatically implemented. Numerical examples indicate that for a truss spar platform, the fatigue failure occurs at the stressed places and the intersection of hard tank and truss, which provides an important reference for local structural reinforcement and optimization.