Abstract: To study the mechanical mechanism of self-stressing steel slag aggregate reinforced concrete filled circular steel tube (steel slag aggregate/concrete@circular steel tube) columns, eight specimens including six short columns and two intermediate length columns were designed for axial compression test, the variable parameters, such as the diameter-thickness ratio, expansion rate of steel slag aggregate concrete and length-diameter ratio were considered. The whole failure process of specimens was observed, and then the strain-stress curves as well as the peak stress was obtained. The influence of variable parameters on the mechanical behavior of self-stressing steel slag aggregate/concrete@circular steel tube columns was analyzed. Test results indicate that the short columns under axial load exhibit shear failure while the intermediate length columns experience global flexural buckling failure mode. The stress-strain curves of all specimens are basically similar, which undergo the peak point, descending section, slow rise section and so on. The peak strain and peak stress of all specimens are significantly increased compared with those of common steel slag aggregate concrete, and the improvement effects are more obvious in short columns than those in intermediate length columns. According to the limit equilibrium condition and entire process analysis, the calculation formula of bearing capacity of self-stressing steel slag aggregate/concrete@circular steel tube columns was proposed, and then the stress-strain model of self-stressing steel slag aggregate/concrete@circular steel tube columns was established depending on the experimental data. The theoretical calculation results are in good agreement with test data. The research results can provide reference for further research and engineering application of self-stressing steel slag aggregate/concrete@circular steel tube columns.