Abstract: This study is grounded in the development demands of low-carbon and green buildings and aims to elucidate the load-bearing mechanism and mechanical performance characteristics of square steel tube restrained laminated bamboo composite columns (SBSTs) under axial compression. Using SBSTs as the object of investigation, 24 composite columns and 3 laminated bamboo reference columns were designed and fabricated. Under both full-section loading and core-section loading schemes, the influences of steel tube wall thickness and strength on axial compression failure modes, load-bearing capacity, initial stiffness, ductility, and energy dissipation capacity were systematically examined. Prediction equations for axial compressive strength and full-range stress-strain models were proposed. The experimental results demonstrate that square steel tubes provide effective lateral confinement to the laminated bamboo core, markedly suppressing radial expansion and thereby enhancing axial compressive performance. With increasing tube wall thickness and steel strength, the peak axial load capacity and initial stiffness of the full-section specimens increased by approximately 64.8% and 69.5%, respectively. By introducing an effective confinement coefficient, a clear linear relationship was established between the axial compressive strength and the lateral confining stress of SBSTs. Furthermore, based on the Richard-Abbott theoretical formula and the synergistic compression characterization method for steel tubes and bamboo, a stress-strain curve prediction model suitable for full-section and core axial compression loading was established. The model maintains a prediction error of less than 10% for peak stress and accurately describes the entire mechanical behavior of the composite column from the elastic stage to the softening stage under different loading conditions.