The invention discloses a modified graphite nanoflake heavy anti-corrosion coating and a preparation method thereof. The coating is prepared from the following components of acrylate polyurethane resin, a graphene nanoflake, a modifier, benzofuran and a drier at the mass ratio of 100:(1-5):(2-10):(30-50):(0.1-0.3). According to the heavy anti-corrosion coating, hydroxyl in the acrylate polyurethane resin is combined with the modified graphene nanoflake, so that oxygen-containing functional groups in the system are increased, and thus the cross-linking degree of the coating is improved, the impedance value of the coating can reach 10<7>-10<9>ohm and the coating has good electrochemical corrosion resistance.