Fly ash-based geopolymer (FAG) possesses extremely low electroconductivity (0.00086 S/m). A new study indicates that graphene could be used as an electron acceptor to improve electroconductivity of geopolymer. In this paper, an electroconductive graphene (GR)/fly ash-based geopolymer (GR/FAG) composite was synthesized by assembly of graphene into the matrix of alkali-activated fly ash-based geopolymer for first time. The results showed that the electroconductivity increased by 348.8 times when adding 1 wt% GR in FAG. The electrochemical impedance of 1.0GR/FAG was much smaller than that of the pure FAG. The N-2 adsorption-desorption isotherms indicated that the graphene could effectively improve the microstructure and pore parameters of FAG. The SEM and EDS results displayed the flake graphene was covered by amorphous fly ash-based geopolymer gels. The XPS results demonstrated that the C-C/C=C binding energy was predominant surface state. The results of UV-Vis-DRS and PL spectra revealed that the absorption onsets of GR/FAG composites were red-shifted and the photoluminescence intensities progressively decreased with increasing graphene content. The photocatalytic degradation of indigo carmine dye was positive correlation with the electroconductivity of GR/FAG composite, and underwent a degradation mechanism of hydroxyl radical.