Abstract: Aiming at the features of thermal stress existing in dissimilar heat surface tube coils, calculations were performed to the thermal expansion stress using finite element analysis, such as linear-elastic small-deformation, linear-elastic large-deformation and elastic-plastic large-deformation method. Above analysis results were used to evaluate the strength and fatigue life of dissimilar heat-surface tube coils, so as to widen the range of their applications. Analysis results show that the thermal stress calculated by the elastic-plastic large-deformation method is closer to actual values; Application results show that the analysis method of linear-elastic large deformation may help to ensure long-term operation of the boiler.