Abstract: The use of slag fly ash based geopolymer instead of cement for soil solidification should be based on the available industrial waste production and engineering construction strength requirements in each region, and a reasonable ratio of slag fly ash based geopolymer should be selected according to local conditions. Based on this, this article uses blast furnace slag (GGBS) and fly ash (FA) as raw materials, with sodium silicate as the alkaline activator, to study the effects of activator modulus and dosage, solidification material dosage, and curing age on the strength of geopolymer stabilized soil under different ratios of blast furnace slag and fly ash. The experimental results show that different GGBS: FA ratios correspond to different optimal water glass moduli. The optimal water glass moduli corresponding to GGBS: FA=GGBS∶FA=8∶2, 6∶4, and 5∶5, are 1.2, 0.9, and 0.9, respectively; The optimal dosage of activator for geopolymer stabilized soil under different GGBS: FA ratios is 15%; When the curing material is 20% at the optimal activator modulus and dosage, GGBS∶FA=8∶2, 6∶4, and 5∶5, the strength of geopolymer stabilized soil at all ages is higher than that of cement stabilized soil. At a curing age of 90 days, the highest strength of geopolymer stabilized soil can reach 16.19 MPa; A prediction model for the unconfined compressive strength of slag fly ash based geopolymer stabilized soil was established based on the relationship between the strength of geopolymer stabilized soil and the ratio of raw materials, the dosage of solidified materials, and the age, which can consider GGBS: FA, the dosage of solidified materials, and the age. The applicability of the model was verified. Through microscopic analysis, it is found that sodium silicate stimulates GGBS and FA to produce gel and soil particles to form a skeleton structure together, which enhances the strength of geopolymer stabilized soil. Increasing the proportion of GGBS in the solidified material can effectively improve the strength of geopolymer stabilized soil. The hydrated calcium aluminosilicate gel (C-(A)-S-H) generated by it makes the soil structure more dense, while the hydrated sodium aluminosilicate gel (N-A-S-H) formed by increasing the proportion of FA cannot effectively bond the soil particles to improve the strength of solidified soil.