This report presents the development of graphene-based nanocomposite coatings on the fiber reinforced composites to improve the coating resistance against the corrosion and other environmental weathering. Graphene nanoflakes were initially functionalized through a silanization process, and then dispersed well into the polyurethane primer and top coats at 0, 2, 4 and 8wt% using high speed agitation and sonication processes. The dispersed nanocomposite coatings were an air sprayed on the surfaces of the composite coupons at different thicknesses, and cured prior to the alternative UV and salt fog exposure tests for 20 days. The performance analyses of the nanocomposite coatings were carried out using atomic force microscopy (AFM), Fourier transform infrared spectrometer (FTIR), thickness measurements, water contact angle, and electro-chemical impedance spectroscopy tests. The test results indicated that the silanization process on the graphene nanoflakes significantly improved the corrosion resistances of the nanocomposite coatings when compared to the non-functionalized graphenes. This study may be useful for the performance improvements of many coatings on the composite aircraft, wind turbines and other applications.