Abstract: To research the utilization of slag and fly ash in the geopolymers, geopolymers were synthesized from slag and fly ash, which were activated by mechanical grinding and activators.The effects of the ratio of slag and fly ash, water cement ratio and the modulus of water glass on the compressive strength of geopolymers were investigated by orthogonal experiment.The microstructure of the samples was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM).The results show that the highest 28-day compressive strength of geopolymer samples is 68.45MPa when the ratio of slag and fly ash is 1∶1, the water cement ratio is 0.4 and the modulus of water glass is 1.2.XRD and SEM analysis of samples prepared under the optimum experimental conditions indicated that the more amorphous aluminosilicate was generated, and the partial crystals gradually transformed into amorphous gelatinous substances with increasing curing age.The incompletely reacted slag and fly ash are closely cemented by the gelatinous substances to form compact internal structure in samples, which promotes the compressive strength of samples.