Abstract: To address the difficulty in evaluating the overall thermal-mechanical response of a large pressure vessel, a fluid-solid-thermal sequential coupling analysis method for complex vessels is proposed. In this method, the convective heat transfer boundary on the wall is determined by segmented flow field calculations, and a differentiated thermal boundary mapping strategy is established according to typical structural forms such as internal insulation, thermal decoupling and water cooling. The temperature field, pressure difference, gravity and support friction loads are then introduced into the finite element model of the pressure vessel. Taking a high-temperature working condition as an example, the temperature, displacement and stress distributions of the key sections of the vessel are obtained. The results show that the proposed strategy retains the main flow and heat transfer characteristics while controlling the computational scale, and thus provides a basis for the iterative structural design and the deformation accuracy control of the pressure vessel.