Abstract: To investigate the mechanical properties of the newly-developed heavy-load short steel tube column reinforced with structural steel and concrete, the stress states of the three different components of the column were analyzed according to the nonlinear relationship between concrete's compression resistance and side pressure. Based on the ultimate equilibrium theory, the ultimate cross-section bearing capacity formula of the column under axial-load was given. Moreover, the main influencing factors on increasing the axial-load bearing capacity were analyzed to determine the relationships between the stress of different components and hoop confining index. The calculated results conform highly with the tested values as shown in earlier works. The hoop confining index and steel quantity used in the column play indispensable roles in enhancing the axial-load bearing capacity, which offers a theoretical basis to the design in engineering applications.