The chloride binding capacity of cementitious materials is a key factor affecting the service life of marine concrete structures. Calcium nitrite was selected as additional calcium phases, and metakaolin or nano alumina was selected as additional aluminum phases. The effects of Ca-Al phases on hydration products, chloride binding capacity and macro performance of alkali activated slag cementitious materials were investigated. The results show that the addition of Ca-Al phases effectively promotes chemical reaction, and improves the chloride binding capacity of alkali activated slag cementitious materials. Compared with control group, the amount of binding chloride increases by 11.5%~34.8%. m(Ca)/m(Al) value in system has an important influence on chloride binding capacity. The decrease of m(Ca)/m(Al) value results in the increase of the content of AFm phases, C-(A)-S-H gels and other products. The content of calcium nitrite has an optimum value. Excessively high content of calcium nitrite negatively affects the strength, but nano alumina compensates for the strength loss. In general, the relative content of Ca-Al phases is important for phase composition and chloride binding capacity of alkali activated slag.