In cement-based composite materials, the issue of graphene oxide (GO) dispersion has long been a bottleneck for its widespread application. In this context, polycarboxylate superplasticizer (PCS) was used to modify GO through a simple preparation process, resulting PCS@GO, which could greatly improve the dispersity of GO. It was found that PCS@GO can be uniformly dispersed in the cement mortar, a phenomenon attributed to the steric hindrance and electrostatic repulsion generated on the GO surface modified by PCS, effectively preventing the aggregation of GO. Moreover, the addition of PCS@GO significantly enhances the mechanical properties, fatigue resistance, and fluidity of the cement mortar while reducing the crystal size of the hydration products, which enhances the overall performance of the cement-based composite material. Based on the above results, this research provides theoretical support and experimental validation for the development of high-performance cement-based composite materials doped with modified GO.