<p>This study investigates the axial compression behavior of lightweight concrete-filled circular aluminum alloy tubular (LCFAT) stub columns for structural lightweighting applications. Nine groups of specimens with varying parameters were tested to examine the effects of the cross-sectional aluminum ratio and a confinement factor on the load-carrying capacity, axial stiffness, and failure modes. To induce ideal failure patterns under axial loading, the specimens were locally wrapped with carbon fiber reinforced polymer (CFRP) at both ends solely to provide end restraint and ensure uniform load transfer; the CFRP was not part of the load-carrying system. The experimental program is complemented by calibrated three-dimensional finite element analyses, which were further employed to conduct parametric studies on concrete strength, alloy yield strength, and tube wall thickness. Based on classical concrete-filled steel tubular (CFST) theory, a strength design model tailored to the aluminum–lightweight concrete interaction is formulated by introducing an elastic modulus reduction factor and a lateral confinement reduction factor. The proposed model captures the key characteristics of the axial response, and the numerical simulations were used to replicate the observed failure patterns and load–displacement curves, supporting an interpretation of the confinement mechanism and behavioral phases. These results provide a theoretical basis for engineering application and design optimization of lightweight composite columns.</p>