Abstract: The stress due to thermal loads after LOCA is indispensable in the design of concrete containment vessel (CCV). As the temperature variation is instantaneous, and the temperature field distribution is non-uniform, the internal force calculation is very complicated. Detailed calculation method and design approach have not been proposed in current CCV design code in China. In this paper, based on heat transfer theory, temperature field distribution in CCV walls at different time after LOCA has been calculated, which could provide the basis for temperature-induced internal force analysis; on the basis of shell mechanics, a simplified calculation method of the internal force due to thermal loads after LOCA in CCV structure has been proposed. According to finite element analysis with ANSYS, a detailed analysis of stress, displacement, and internal force of CCV due to thermal loads in each time after LOCA has been performed. A comparison between the theoretical result and the finite element result demonstrates the accuracy of the proposed method.