Abstract: According to Technical Specification for Steel Tube-Reinforced Concrete Column Structure, the compression-bending capacity of a steel tube-reinforced concrete composite column without considering the steel tube is not fully utilized. Therefore, the failure pattern and confinement mechanism through eccentric compressive test was performed to complement the existing calculation theory in this paper. The test results show that failure patterns of all specimens are divided into two types, namely the large and the small eccentric failures, whose demarcation failure criterion is that the tensile reinforcements reach the yield strength and the concrete compressive edge reaches the ultimate compressive strain. Furthermore, the cross-section strain obeys the plane section assumption, and the transverse strain of steel tube increases with the decreasing of eccentricity, which fails to yield at the peak loading and is not negligible. Finally, a formula is proposed to calculate the compression-bearing capacity considering the influence of steel tube and its restraining action. Based on 40 groups of test data from this paper and other references, this calculated formula proves to be reasonable, and can be used to guide the design for steel tube-reinforced concrete composite column.