Functionalized graphene (G-MA) was prepared by a facile wet ball milling strategy, which achieved exfoliation and functionalization of graphite simultaneously. The G-MA showed excellent dispersion in water and polar solvents. Thus, a G-MA coating was prepared from G-MA in mixed solvents (H₂O–ethanol) without binder or surfactant. The scanning electron microscope (SEM) images of the G-MA coating exhibited a smooth and flat surface. The G-MA coating showed a conductivity of 769 S m⁻¹ at room temperature, and a big increase could be found at 2000 S m⁻¹ after thermal treatment under 200 °C for 2 h, indicating the restoration of the conjugated structure via the reverse Diels–Alder reaction. This synthetic method of functionalized graphene offers a powerful strategy for the reversible modification of the graphene electronic properties, which may expand their usage.