In the process of using biomass for power generation in power plants, the composition and properties of the incineration slag generated by different incineration processes are different, which poses significant challenges for its resource utilization. In this study, autoclaved aerated concrete (AAC) was prepared using biomass slag, cement and lime as the main raw materials. The effects of slags generated by two mainstream biomass incineration processes on the slurry properties and mechanical properties of AAC products were studied. Hydration products and micromorphology of AAC were also systematically studied by SEM and XRD. The results show that with the addition of mechanical grate incinerator slag (MGI), the initial fluidity decreases significantly, the fluidity loss of slurry increases, the gas volume decreases and the specific strength of AAC increases first and then decreases. When the MGI mass fraction is 28%, it is the best dosage to take into accont the strength and density of ACC, with the compressive strength and density are 3.6 MPa and 593.22 kg/m3, respectively. Due to the presence of a large amount of anhydrite and free calcium oxide in circulating fluidized bed combustion slag (CFBC), the solidification and hardening of the slurry are affected. With the increase of CFBC content, the initial fluidity of AAC slurry gradually increases, the gas generation volume increases， and the specific strength of AAC test blocks continues to decrease. In addition， the morphology and bulk density of tobermorite, hydration product, in AAC have a significant impact on the mechanical properties of the product.