Abstract: The ultra-high performance concrete (UHPC) - normal strength concrete (NSC) composite pier has the prominent mechanical performance advantage and the promising engineering application prospect. At present, the lack of corresponding design method seriously hinders its practical engineering application. An experiment was conducted to evaluate the hysteretic behavior of the composite pier under cyclic loading. The influence of the thickness of UHPC shell was investigated. Test results show that the bearing capacity and the energy dissipation of the composite pier obviously increase with the increase of the thickness, while it increases first and then decreases in compression damage, in bearing capacity degradation rate and in ductility, etc. Based on the test results, the model of composite section is established, and the influence of parameters such as the thickness is discussed. The yield moment and yield curvature are proposed, and the mechanism of shell thickness is revealed. The optimal design of the composite section is carried out to optimize the compression contribution ratio of NSC and maximize ultimate curvature, and then the optimal shell thickness is recommended. It ensures that the UHPC performance is fully utilized, meanwhile the composite section has a larger ultimate curvature and the composite pier has a better deformability. A support is thusly provided for engineering application of the composite piers.