Abstract: This is an article in the field of inorganic non-metallic materials.To achieve comprehensive utilization of fly ash and sintering red mud, this study uses fly ash as the main raw material, sintering red mud as an auxiliary material, and sodium hydroxide as an alkaline activator to synergistically prepare geopolymer. The results showed that the optimal preparation conditions for geopolymer were as follows: fly ash was pretreated with a classification pretreatment (extraction of fine fraction), with a graded particle size of 37 μm. The mass ratio of fine-grained fly ash to sintering red mud is 7∶3 (g∶g), and the dosage of NaOH accounts for 15% of the mass of the precursor powder. The compressive strength of the geopolymer prepared at these conditions reached 35.52 MPa after curing at room temperature for 28 d, meeting the strength standard of 32.5R slag portland cement in the Common Portland Cement of China. The raw materials and geopolymers prepared at different pretreatment methods were analyzed and tested using XRF, XRD, ICP-OES, and SEM-EDS. The test results showed that compared to mechanical grinding, classification pretreatment can effectively improve the reactivity of fly ash, allowing more active silicon and aluminum components to participate in geopolymerization reactions. The addition of sintering red mud can promote the formation of calcium-rich aluminosilicate gel and densify the microstructure of geopolymers. This study provides new insights into the comprehensive utilization of fly ash and sintering red mud.