Ground granulated blast furnace slag(GGBFS) was used to substitute for part of metakaolin, to obtain the cementitious material being able to cure at ambient temperature. The technical methods of XRD, FTIR, and SEM were employed to study the reaction mechanism of the metakaolinGGBFS compound material. The results show that the viscosity and the curing time of the alkaline activated paste will be reduced by adding GGBFS into metakaolin. The hardened binder with substantial compressive strength can be obtained by activating the compound of metakaolin and GGBFS at ambient temperature. The results by XRD and FTIR reveal that the N A S H gel by geopolymerization of metakaolin and the C S H gel by hydration of GGBFS are generated simultaneously during the activation process of the compound system. The activator modulus(SiO2Na2O ratio) and the mass ratio of metakaolin and GGBFS are the prime factors which influence the mechanical properties of reaction products, because the compressive strength of hardening paste decreases with the increase in activator modulus when the mass ratio of GGBFS is less than 40%, while it increases with the increase in activator modulus when the GGBFS ratio exceeds 60%.