Abstract: Coal gasification slag is a by-product produced in the process of coal gasification, and a large amount of landfill has caused great environmental pollution. Therefore, red mud and carbide slag were used to synergistically stimulate the activity of coal gasification slag and slag to prepare coal gasification slag-based geopolymer filling cementitious materials. The mass ratio of coal gasification slag to slag, the mass ratio of carbide slag to red mud, the grinding degree of coal gasification slag, and the macroscopic properties of coal gasification slag-based geopolymer under curing humidity were studied. XRD, SEM-EDS, TG-DTG, FT-IR, LF-NMR and other methods were used to reveal the microstructure of geopolymer. The results show that when the curing humidity is 95%, the content of coal gasification slag is 30%, and the red mud : carbide slag is 2 : 3, the excitation effect is better, and the 28 d compressive strength can reach 11.781MPa. The main hydration products of coal gasification slag-slag synergistically activated by carbide slag-red mud are N/C-A-S-H gel, calcium hydroxide (CH) and calcium carbonate. The increase of grinding degree of coal gasification slag and slag content can improve the depolymerization of silicon-aluminum glass in the precursor. The increase of carbide slag content increases the concentration of OH⁻ and Ca²⁺ in the solution. The 95% curing humidity ensures the hydration environment and promotes the formation of N/C-A-S-H gel phase. Calcium carbonate can fill the pores and form a dense gel matrix together.