Silica fume aluminum oxide geopolymer was prepared and its mechanical properties were investigated through orthogonal test. Results show that the properties of geopolymer are determined by the concentration of alkali activator， the molar ratio between silicon and aluminum and the type of alkali activator. It is recommended that the concentration of alkali activator is 3.0 mol/L， the ratio between silicon and aluminum is n（SiO2）/n（Al2O3）=4， and the best suitable alkali activator is potassium hydroxide. It is observed that flexural strength and compressive strength of geopolymer are 7.17 MPa and 17.15 MPa respectively when the concentration of potassium hydroxide is 3.6 mol/L.