Abstract: The concrete-filled corrugated steel tubular (CFCST) column is a novel steel-concrete composite column characterized by transverse corrugated steel plates. This unique application of the plates leverages their considerable out-of-plane stiffness, markedly enhancing the compression performance of CFCST columns while significantly reducing steel material consumption. However, the exact confinement mechanism of the corrugated steel on the infilled concrete remains unclear. To address this question, we analyzed the confinement effect of the CFCST columns under axial compression. The lateral displacement, lateral stress, and bending moment distributions were determined through differential equations, and parametric analysis was performed to examine the impact of varying corrugated steel plate dimensions and concrete strength on these distributions. The results indicated strong confinement effects at the boundary positions with virtually no effect at the mid-span. The stiffness of the corrugated steel plates and the confinement effect were found to be directly proportional. Additionally, a relationship was established between the average lateral stress of the concrete and the effective confinement coefficient of the CFCST thorough data fitting, leading to a design formula for calculating the axial compression capacity of CFCST columns. Finally, the accuracy of the formula and its applicability in engineering design were confirmed through validation on experimental data, with the maximum deviation being within ±5%.