Hardened alkali-activated slag cementitious materials contain plenty of gel pores. The electrical double layer (EDL) on the gel pore surface can obviously affect the chloride transport rate. This paper describes the features of the EDL on the solid-liquid interface in alkali-activated slag cementitious materials. The zeta potential under different concentrations of chloride ions and surfactants was measured and analyzed. Mechanisms of the EDL effect on chloride diffusion and adsorption were elaborated. Results show that the alkali-activated slag cementitious materials had a negative zeta potential and its value would become less negative with a rise in chloride concentration. Utilizations of cationic surfactants resulted in reversal of the zeta potential toward a positive value, whereby the chloride binding ability was increased and the effective chloride diffusion coefficient was reduced. An opposite impact was observed by making use of anionic surfactants. In alkali-activated slag cementitious materials changes of the EDL effect at pore surface can alter the chloride binding capacity by an order of 50% or more.