Disclosed are an anticorrosion coating for a metallic ground grid and a preparation method thereof. According to the preparation method, steel and aluminum alloy are used as base materials, a copper-stannum composite coating is prepared by the method of chemical plating, and the thickness of the coating is controlled by adjusting solution composition and technological parameters of plating. The method is characterized in that: every liter of a displacement copper plating solution contains 25 to 100 g of phytic acid copper, 10 to 20 g of tartaric acid, 0.5 to 5.0 g of additive A and 10 to 30 gof additive B, wherein additive A is at least one selected from the group consisting of 8-hydroxyquinoline, benzotriazol and thiourea, and additive B comprises sulfosalicylic acid, sodium dodecyl benzene sulfonate, asccharin and polyethylene glycol; every liter of a displacement stannum plating solution contains 25 to 50 g of stannous sulfate, 100 to 200 g of sulfuric acid, 20 to 30 g of citric acid and 20 to 45 g of sodium hypophosphate. The aggregate thickness of the copper-stannum composite coating in the invention is 40 to 50 mu m. The invention has the advantages of a simple process, convenient operation and energy conservation, and is particularly suitable for anticorrosion treatment of welding and metallic ground grids with a complex structure.