Graphene (G) and graphene oxide (GO) have been shown to significantly improve the mechanical properties of cement-based materials. In this study, the effect of the G/GO on cement hydration was investigated. First, the zeta potential of G/GO in simulated solutions was tested, and the interaction between G/GO’s surface and Ca was explored. Subsequently, scanning electron microscopy was used to observe the morphology of C–S–H nucleation and growth on the cement surface in the cement paste containing G/GO. Furthermore, XRD and TGA analyses were carried out on the hydration products of the sample. At last, isothermal calorimetry was applied to investigate the influence of G/GO on the early hydration of cement. The results showed that the addition of G/GO significantly accelerates C–S–H nucleation and growth on the cement surface. It is indicated that the high mobility ions derived by G/GO in the cement paste dominate the reason for the accelerated hydration of cement. The presence of G, especially GO, facilitates the mobility of ions, especially Ca , thus enhances the interaction between the cement surface and the ions. This strong interaction promotes the C–S–H nucleation and growth, and therefore, the hydration of the cement. (1) GO has a strong interaction with Ca . (2) G/GO accelerates C–S–H growth. (3) High mobility ions derived by G/GO facilitate hydration.