Abstract: The steel box-steel tube concrete composite tower is a novel tower structure designed for the application in ultra-long-span suspension bridges. The cross-section of this tower features four internal steel tube concrete columns primarily responsible for bearing axial loads, while an external steel box mainly resists bending moments. The steel tube concrete columns are interconnected with each other and with the steel box through web plates and diaphragms, forming an integrated structure. This study conducts experimental research to investigate the load-bearing capacity, failure modes, ductility, and energy dissipation capabilities of the composite tower under cyclic compressive and bending loads. It also examines the coordinated deformation capacity of the composite tower's cross-section. The experimental results and simulation analyses indicate that the failure mode is characterized by the local buckling and fracture of the external steel box at the base, with minimal deformation observed in the internal steel tube concrete columns. The cross-section at the base of the composite tower deviates from a plane section after deformation, whereas other cross-sections approximately maintain a plane-section configuration, indicating that the collaborative working performance between the steel box and the steel tube concrete is good. Based on the experimental and analytical findings, a simplified calculation method for the compressive-bending load-bearing capacity of the composite tower is proposed. This method divides the tower section into an external steel structure and an internal concrete-filled steel tubular lattice column, yielding results that are both accurate and conservatively safe.