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Lime is one of the main raw materials necessary for the production of autoclaved aerated concrete (AAC). The preparation of lime through calcining limestone directly/indirectly emits large amount of CO2 due to the limestone decomposition and energy consumption. In this study, AAC was proposed by using modified carbide slag (MCS) instead of lime, which can effectively utilize solid wastes and reduce the CO2 emission. Results showed in the first two hours of hydration, the heat release rate of MCS was higher than that of lime, and the cumulative hydration heat of lime and MCS within 30 h is 206.1 J/g and 204.3 J/g, respectively. MCS can not only improve the fluidity of slurry, but also enhance the gas-foaming rate. Cumulative pore volume increased with the increase of MCS content in AAC. Tobermorite, quartz, katoite, anhydrite and calcite are the main minerals in AAC. With the increase of MCS content, the density and strength of AAC decrease and the thermal insulation performance increase. When the MCS content is 100%, the AAC density is 594 kg/m3, the compressive strength is 3.6 MPa and the thermal conductivity is 0.141 W·m− 1·K− 1, meets B06 A3.5 in Chinese standard GB 11968 − 2019.