Sodium water glass alkali-activator was used to prepare fly ash and slag base polymer concrete (GC). The effects of different alkali-activator moduli (1.2, 1.4, 1.6), sand rates (0.3, 0.35, 0.4) and fly ash to ash to slag ratio (4:6, 5:5, 6:4) on the mechanical properties of compressive and splitting tensile strengths of GC at different ages were investigated. The results showed that the compressive and splitting tensile strengths of GC increased and then decreased with the increase of alkali-activator modulus, and the best mechanical properties were obtained when the alkali-activator modulus reached 1.4. With the increase of ash to slag ratio, the compressive and splitting tensile strength of GC were decreasing, and the best mechanical properties were obtained when the ash to slag ratio reached 4:6. The compressive and splitting tensile strengths of GC did not change significantly with the increase of sand ratio. The optimum mix ratio was alkali-activator modulus of 1.4, sand rate of 0.35, and ash to slag ratio of 4:6. The influencing factors on the properties of geopolymer concrete were ranked as: ash to slag ratio>alkali-activator modulus>sand rate.