Abstract: In order to investigate the bias mechanical behavior of the new materials composite of alkali-activated slag concrete -filled steel tubular(AASFST) columns under eccentric load,four middle long columns of AASFST were made with different expansive agent dosage and the eccentricity to do mechanical property test under eccentric load. The experimental results showed that the stress damage process can be divided into five stages: linear elastic stage, non linear elastic stage, elastic-plastic stage, plastic stage and failure stage. Under the condition of the same eccentricity, the elastic working stage of AASFST column can be extended by the addition of expansive agent, meanwhile its ultimate bearing capacity was improved too; Under the condition of the same expansive agent dosage, the elastic working stage of AASFST column was shortened, and its ultimate bearing capacity decreased nonlinear, strain and lateral deflection increased; the value 0.275 of confined effect coefficient v can be seen as the boundary value of the elastic working stage and the elastic-plastic working stage of the test.