Abstract: In the present paper, the modified Hummers method was used to prepare the suspension of graphene oxide (GO). The structure and size of GO crystal were characterized by FTIR, XRD and AFM. By measuring the compressive strength, flexural strength and investigating the morphology of composite materials, the influence of the content of GO and water-cement ratio on the mechanical properties and microstructure of graphene cement-based composites have been systematically discussed. Test results indicate that flexural and compressive strengths of the graphene cement-based composites increase first and then decrease with the increase in GO content, and the growth rate of flexural strength is much higher than that of the compressive strength. The flexural strength of composites reaches the maximum value of 13.72 MPa when the optimal additive amount is 0.03%. The strength enhancement of cement mortar with GO under high water-cement ratio is more significant than that under relatively low water-cement ratio. The microstructure of cement-based composites material was characterized by SEM. It is found that GO can optimize the microstructure of cement hydration products, refine the crystal size and form a more dense and uniform network structure, and thus improve the macroscopic properties of cement-based materials.