Abstract: In order to figure out the effect of spherical-cap gaps on the performance of the axially loaded elliptical concrete-filled steel tube (ECFST), this paper conducts an experimental study on the axially loaded ECFST columns with spherical-cap gaps (ECFST-SG). The development rules of the failure mode, axial compressive resistance, initial stiffness and ductility of ECFST-SG column under the influence of spherical-cap gap ratio are analyzed. The strain distribution at mid-height cross-section and strength feature of the core concrete are revealed respectively. According to the mechanism of gap imperfection on the confining stress of core concrete, the confining division theory of the core concrete section is proposed, and the calculation formulae for predicting the axial compressive resistance of ECFST-SG columns is deduced and validated. The results indicate that the failure modes of the axially loaded ECFST-SG columns mainly include crushing and shear failure of the core concrete, outward and inward buckling of the steel tube, and excessive lateral deflection of the overall specimen. The spherical-cap gap may weaken the interaction between the elliptical steel tube and the core concrete distinctly, hence the axial resistance, initial stiffness and ductility of ECFST stub column will be reduced.