Abstract: Solar radiation is an important environmental factor which affects the nonlinear temperature distribution of concrete filled steel tubular (CFST) sections and then causes interfacial debonding, while the use of a core expansive concrete is a significant method for optimizing the interfacial performance of CFST elements. In this paper, eight CFST specimens with different expansion agent dosages were designed, their interfacial performances under solar radiation were investigated using a solar radiation simulator, and the temperature and strain time-histories of the steel tube and core concrete and the sectional temperature gradient mode along the direction of the incoming light were analyzed. Then the impacts of concrete self-stress on the sectional temperature stress, the sectional radial stress caused by radiation effect, and the position and size of the interface gap under solar radiation were investigated using heat transfer theory and a finite element method. The results show that the concrete self-stress can effectively improve the interfacial mechanical performance of CFST under solar radiation and help avoid interface debonding caused by large temperature stress gradients at the different sectional positions; it also exerts a definite influence on the interfacial gap positions and size of CFST under