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.