Abstract: Testing methods including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform-infrared spectroscopy (FT-IR), and thermogravimetric/differential scanning calorimetry (TG-DSC) were used to study the reaction mechanism of aerated concrete prepared by iron ore tailings (IOTs) under the condition of autoclaved curing. Without autoclaved curing, major hydration products in the green body are ettringite (AFt), calcium silicate hydrate (CSH) gels with low degree of crystallinity, and Ca(OH)2. The XRD peaks of some minerals in the iron tailings reduce. After autoclaved curing, the XRD peak of ettringite disappears, but the XRD peak of tobermorite increases. It is revealed that, mineral components in the iron railings are decomposed, and reactions between the active components of SiO₂, Al₂0₃, and Ca(OH)₂ cause the formation of tobermorite under the conditions of high temperature, high pressure and hot alkaline activation.