In this study，silica fume and fly ash used to improve the mechanical properties，hydration reaction and microstructure of slag-based geopolymer were disscussed.The effects of different proportions of silica fume and fly ash on the mechanical properties of the geopolymer mortar were studied，and the hydration mechanism and microstructure were analyzed by XRD，FTIR and SEM.The research showed that the effect of 10% silica fume and 1.2 and 25% sodium silicate was the best，and the compressive strength of 3，7 d and 28 d could reach 54，68 MPa and 72 MPa，while the effect of fly ash was poor，and the effect of 3，7 d and 28 d was better when the content was 10% and 1.2 and 25% of sodium silicate.The strength was 53，58 MPa and 62 MPa respectively.The addition of silica ash filled the pores of the geopolymer of the slag-based，and a large amount of SiO₂ reacted with OH^-，resulting in the Si—O bond fracture reaction to form calcium silicate aluminate hydrate［C-（A）-S-H］ and sodium silicate aluminate hydrate［N-（A）-S-H］ gels，which improved the mechanical properties，hydration reaction and microstructure of the geopolymer of the slag-based.However，excess silica ash would restrict the formation of gel，resulting in decreased compressive strength.The compressive strength of pure slag ground geopolymer for 7 d and 28 d was increased by 23.6%，9.1% respectively.Due to the activity and low calcium content of fly ash，the incorporation of fly ash hindered the hydration reaction of the geopolymer in the slag-based and the microscopic cracks were larger.Therefore，the combination of silica fume and slag could produce the high strength geopolymer cementing materias.