AbstractCoal mine filling requires a safe, lightweight, and high-strength filling material, but current commonly used aeration agents, such as hydrogen peroxide, which produces the combustible gas O2, and aluminum powder, which produces the explosive gas H2, are not suitable for coal mine filling. In this paper, a new inorganic composite aeration agent, namely sodium bicarbonate and potassium aluminum sulfate, which produces inert gas CO2, was developed. The effects of this composite aeration agent admixture (at contents of 0%, 2%, 4%, 6%, and 8%) on the properties such as fluidity, setting time, compressive strength, and water resistance of sulfoaluminate cement paste with high water-to-cement ratios were investigated systematically. The evolution of the microstructure and pore structure of this foamed material was determined using X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA), and scanning electron microscopy (SEM). The results showed that when the amount of aeration agent was 8%, the 7-day compressive strength of the prepared sulfoaluminate cement–based foamed material with a dry density of 600 kg/m3 was 1.2 MPa. Compared with the control group, the setting time was shortened by 87%, dry density was reduced by 42.1%, 7-day compressive strength was increased by 47.5%, and water resistance was increased by 45.4%. The composite admixture not only formed uniform bubbles within the sulfoaluminate cement paste but also produced in situ calcium carbonate, which promoted the hydration of sulfoaluminate cement and made the microstructure of the hardened paste denser. The results provide new materials for coal mine foam filling, which can be applied to corner gas control and foam filling in mining areas and coal mine fire prevention.