The invention provides an anticorrosive and environment-friendly coating material applicable to drilling fluid and a preparation method thereof. The coating material is prepared from a dopamine modified boron carbide grafted amino group. The preparation method of the anticorrosive and environment-friendly coating material applicable to the drilling fluid comprises the following step of introducingthe amino group through reaction between a silane coupling agent and hydroxyl on the surface of polydopamine, so as to enhance the interface acting force between boron carbide and epoxy resin; the dispersity and interface mutual combination of the boron carbide on the epoxy resin are improved, so that the anti-corrosion performance of the epoxy resin is enhanced. According to the anticorrosive and environment-friendly coating material applicable to the drilling fluid, prepared by the preparation method provided by the invention, the dispersity in an epoxy resin matrix is enhanced by a boron carbide surface grafting chain, so that the anticorrosive performance of the epoxy resin is effectively improved; meanwhile, compared with pure epoxy resin, the anticorrosive and environment-friendly coating material applicable to the drilling fluid is used as a composite coating and the anticorrosive performance is improved. Especially, the anticorrosive and environment-friendly coating material applicable to the drilling fluid is applicable to anticorrosive protection of metal sleeves and drilling tools in the high-temperature, high-pressure and high-mineralization-degree drilling fluid.