Abstract: In order to improve the mechanical properties of coal gangue geopolymer concrete and explore its engineering application potential, geopolymer concrete was prepared with coal gangue and slag as raw materials, and the effects of single addition and mix addition of nano-SiO₂ (0~2.5%, mass fraction) and steel fiber (0~1.25 %, volume fraction) on the mechanical properties of geopolymer concrete were studied. Further more, the microstructure of geopolymer concrete was studied by SEM to help analyze the modification mechanism. The results showed that the mechanical properties of geopolymer concrete can be significantly improved by adding appropriate amount of steel fiber or nano-SiO₂, and the effect was better when the two were mixed. In terms of compressive strength, nano-SiO₂ modified effect was better than steel fiber, while in terms of splitting, tensile and flexural strength, steel fiber modification effect was better, presumably due to the different mechanism of action of the two. The combination of nano-SiO₂ and steel fiber has better modification effect because nano-SiO₂ not only improves the micro-density of geopolymer gel, but also enhances the bond between steel fiber and matrix. The research results enrich the knowledge system of the properties of nano-SiO₂ and steel fiber modified geopolymer composites, and guide the further application of coal gangue geopolymer concrete.