To achieve low-carbon resource utilization of industrial solid waste, a CO2 mineralization curing test was carried out with steel slag (SS), granulated blast furnace slag (GBFS), and cement as raw materials, to study the effects of pretreatment time and SS-GBFS mixing ratio on the effect of CO2 mineralization curing of cementitious materials and microstructural changes. The results show that appropriate pretreatment can improve the compressive strength of the specimen and the effect of CO2 mineralization maintenance. Under the condition of pretreatment at 60 ℃ for 12 h, the compressive strength of the 50% SS+10% GBFS specimen after CO2 mineralization curing is the highest, while the 40% SS+20% GBFS specimen has the highest carbon fixation rate. CO2 mineralization curing generates a large amount of CaCO3 in specimens, and the mineralization products are mainly calcite and a few aragonite, and the generated CaCO3 crystals make the pore structure of the specimen dense and thus improve the mechanical properties.