Four kinds of graphite derivatives in different exfoliation degrees were synthesized via modified Hummers’ method by controlling the mass ration of graphite and KMnO4. The modified graphite derivatives (GUF) were synthesized through chemical modification with the prepolymer of urea–formaldehyde. Results of Raman spectroscopy (Raman) and Scanning electron microscopy (SEM) revealed that the layer exfoliation was affected by oxidation degree during the preparation of graphene oxide (GO). The highly exfoliated GO was fully modified by UF resin and presented excellent compatibility with epoxy resin. The data of electrochemical impedance spectra (EIS) verified the optimal corrosion resistance of GUF/EP composite coating with the highly exfoliated GO sheets. The data of localized electrochemical impedance spectroscopy (LEIS) demonstrated that the highly exfoliated modified GO exhibited slight galvanic corrosion in the defective coatings.