The effect of retarders, the dosage of steel slag on the properties of alkali-activated steel slag-slag based cementitious materials and the hydration characteristics of complex binding material were studied by the determination of strength and hydration heat evolution as well as type of hydration products and micromorphology of hardened paste. The results show that the properties of the setting time and the strength of binding material, with a composition of steel slag of 40%, blast furnace slag of 60 %, alkali activator of 6% and retarder K of 1%, can match the standard of grade 42.5R ordinary Portland cement. The hydration heat release characteristics of alkali-activated steel slag-slag based cementitious materials are similar to alkali-activated slag cement, and the accumulative heat is limited. Steel slag and slag have a positive interaction, and the combination is beneficial to the development of the hydration process of the system.