Highly active supplementary cementitious materials (SCM) were prepared using fly ash microspheres, granulated blast furnace slag and silica ash via mechanical activation-chemical activation method. The effects of multiple SCM activated by different methods on activity index and hydration products of mortar were studied. The effect of multiple SCM addition on the compressive strength and sulfate corrosion resistance of steamed concrete was discussed. The hydration products and pore structure of materials were analyzed by X-ray diffraction (XRD), thermogravimetric method (TG-DSC) and mercury pressure method (MIP). The results show that by using multiple SCM to replace 30% (mass fraction) of cement, the 3 d, 7 d and 28 d activity index of mortar reach 137.54%, 140.06% and 143.97% after steam curing treatment with resting for 6.0 h and 90 ℃ curing for 4.5 h, respectively. The porosity of the hardened paste is 6.78%, and the decrease ratio of mortar fluidity is 3.94%. When the resting time is 7.5 h and the steam curing time at 90 ℃ is 4.5 h, the compressive strength of concrete for 1 d increases by 17.7% compared with cement group and the sulfate resistance coefficient of concrete increases by 5.8%. When the resting time is 6.0 h, and the steam curing time at 90 ℃ is 4.5 h, 7.0 h and 12.5 h, the compressive strength of concrete for 1 d increases by 13.4%, 16.2% and 15.3%, and the compressive strength for 7 d increases by 16.3%, 16.0% and 15.2% compared with cement group, respectively. The sulfate corrosion resistance coefficient of concrete reaches 90.1%. After the combined mechanical, chemical and hot steam high-temperature activation, the secondary reaction occurs between highly active components in SCM and Ca(OH)2 in cement, promoting the generation of calcium silicate hydrates (C-S-H) gel. Thus, it improves the performance of streamed concrete.