Supercritical boilers as the ‘heart’ of the power system, providing long-lasting navigational power for the entire ship's operation. Due to the continuous switching of working conditions, the fluctuation of the pressure in the drum and the coupling of the temperature field, the continuous effect of the cyclic stress will cause the crack of the steel structure of the drum, resulting in fatigue damage. In this paper, the workbench platform under the ANSYS software was used. The calculation based on the finite element method and the thermal analysis, structural analysis and other analytical tools, get the temperature and stress field of the entire drum under this condition. The numerical simulation results show that the stress level of the drum is unevenly distributed in different regions. The maximum stress point (also called dangerous point) of the entire drum occurs in the first tube of the D30 row in the second row of the radiation zone .At the pressure trough time point (100s), the stress intensity at this point reaches 449.92MPa, while in the upper drum area without the pipe, the stress level is lower and the overall stress intensity is not higher than 100MPa. During the entire 278 seconds, the stress amplitude at the point of danger was 144.17MPa.