In order to obtain the critical thickness of graphite-like carbon coating on 6061 aluminum alloy with the corrosion resistance against proton acid and the reduction value of interfacial contact resistance, a series of graphite-like carbon coatings were deposited on 6061 aluminum alloy plate by a magnetron sputtering system. The microstructure of the deposited coatings was characterized, and the interfacial contact resistance, corrosion resistance, and stability of the coatings were analyzed. Results show that the critical thickness of the graphite-like carbon coating on 6061 aluminum alloy with corrosion resistance against the proton acid in proton exchange membrane fuel cell cathode environment is 0.97 μm. Compared with the ones prepared at low carbon target currents, the coatings prepared at the carbon target current of 4.5 A show a smoother surface. When the carbon target current reaches 4.5 A, the interfacial contact resistance is the lowest, reaching 16 mΩ·cm², which is two times larger than that of the graphite bipolar plate.