The calcium silicate slag-based alkali-activated cementitious materials were synthesized and cured in moist air (MA), sealed air (SA), steam air (HA), respectively. The mechanical properties, reaction products and microstructure were investigated by X-ray diffraction, infrared spectroscopy, thermogravimetry analysis-differential scanning calorimetry, mercury intrusion porosimetry and scanning electron microscopy. The results show that the main reaction products under three curing conditions are calcium alumina silicate hydrategels. The density and mechanical properties varywith curing conditions. The specimens cured in HA exhibitthe densest microstructure and optimum mechanical properties. Compared to MA, the content of reaction products in specimens increases when cured in HA due to the promotion of elevated temperature, giving rise to the optimization of density and mechanical properties. When cured in SA, despite the fact that ahigher temperature contributesto the alkali-activation, as well as adistribution shift of capillary pores to lower diameters, the decrease of inner relative humidity of specimens preventsthe alkali-activation. As a result, it is difficult to increase the density and mechanical properties of specimens cured in SA.