Three types of stearates were used to modify alkali-activated slag（AAS） and the variation of its performance was examined and analysed under sodium sulphate environment. AAS exhibits significant physical crystallisation damage under wet-dry cycles of sodium sulphate. The addition of calcium stearate（CaSt） and sodium stearate （NaSt） can improve the resistance of AAS against physical crystallisation damage of sodium sulphate by decreasing its sorptivity， optimizing its micro-structure， and mitigating its appearance damage in the semi-immersion-wet-dry cycle environment， whereas the potassium stearate（KSt） exacerbates the physical crystalline damage of sodium sulphate of AAS.