Sodium dodecyl sulfonate (SDS) and carboxyl methyl cellulose (CMC) were used as surfactants to prepare Graphene/water nanofluids. These nanofluids as well as Graphene/water nanofluid without surfactant solidified with a static magnetic field, and then melted at room temperature. The zeta potentials, particle sizes, absorbencies, thermal conductivities, solidification and melting photographs were applied to evaluate the dispersion of Graphene/water nanofluids during solidification. It was found that the dispersion of the nanofluid without surfactant was severely destructed during solidification, while the other nanofluids with surfactant obtained relatively good dispersion by magnetic field. But sediments were observed to accumulate gradually over time in the subsequent melting Graphene/SDS/water nanofluid. We thought that CMC and SDS probably improved the dispersion of graphenes in the solidified water by decreasing the contact angle of graphene by water and thus increasing the nucleation rate of Graphene/water nanofluid. External electromagnetic field could further enhance the nanoparticle dispersion in the solidification of nanofluids by driving graphenes to move towards the solidification interface. This dispersion effect of magnetic field was strongly dependent on the amount of surfactant adsorbed on the graphenes. With increasing adsorption amount of surfactant, the dispersion of surfactant-coated graphenes in water became better.