The characristic of electrical double layer（EDL） on the solid-liquid interface in alkali-activated slag cementitious materials were described. The Zeta potential under different concentrations of chloride and surfactant dosages was measured and analyzed. Mechanisms of the EDL’s effect on chloride diffusion and adsorption were clarified. The results show that the Zeta potential of alkali-activated slag cementitious materials is negative， and it becomes less negative with an increase in chloride concentration. Cationic surfactants can convert the Zeta potential to positive value， thereby improving the capacity of chloride adsorption and reducing the effective chloride diffusion coefficient. However， anionic surfactants have the opposite effect. The change of EDL’s effect on the pore surface of alkali-activated slag cementitious materials can alter the capacity of chloride adsorption by more than 50%.