[Purposes] The effect of cement substitution rate on the compressive strength and failure mode of geopolymer-cement solidified soil-rock mixture was studied, and the solidification mechanism of geopolymer-cement on soil-rock mixture was revealed. [Methods] The unconfined compressive strength test, moisture content determination test, scanning electron microscope test， and X-ray diffraction test were used to investigate the effect and the change law of cement substitution rate on the compressive strength, failure mode, moisture content, microstructure， and mineral composition of metakaolin-slag-cement based geopolymer solidified soil and fly ash-slag-cement based geopolymer solidified soil with age. [Findings] When the cement substitution rate is 0%-20%, the compressive strength of solidified soil is proportional to the cement substitution rate. Metakaolin-slag-cement based geopolymer and fly ash-slag-cement based geopolymer have the optimal cement substitution rate of 20%, and the 14 d compressive strength of the corresponding solidified soil can reach 2 510.90 kPa and 2 532.14 kPa, respectively. With the increase of cement replacement rate, the failure mode of solidified soil gradually changes from bulging failure to splitting failure. When the curing time is 14 d, the solidified soil with 20% cement replacement rate has the lowest water content and the most sufficient hydration reaction. The hydrated sodium silicate (N-A-S-H) and hydrated calcium aluminosilicate (C-S-H) gel produced by the reaction play a cementing and filling role in the pores. [Conclusions] An appropriate amount of cement substitution rate can increase the hydration reaction rate, promote the formation of hydration products, and effectively improve the curing effect of geopolymer-cement on soil-rock mixture.