In this study, we study the behavior of CFT subjected to pure bending moment considering the interface character between the materials. We assume that the interface between the materials has 2 cases, one is full-composite the other is non-composite. Through the analysis of the FEM results, we find that CFT’s flexure behavior is unique compared to other composite structures. There is almost similar CFT’s flexure behavior in the pure moment regardless of interface character between steel and concrete. This is because there is no difference in the neutral axis of the full-composite and non-composite in the CFT scetion.