The invention discloses an engine coolant and a preparing method thereof. The engine coolant is prepared from, by weight, 500-700 parts of water, 40-60 parts of sodium formate, 5-15 parts of borax, 0.2-1.5 parts of potassium molybdate, 0.5-1.5 parts of octanedioic acid, 1-10 parts of sodium caprate, 0.5-1.5 parts of sodium nitrate, 0.5-1.5 parts of benzotriazole, 1-3 parts of sodium hydroxide, 1-3 parts of sodium metasilicate nonahydrate, 200-400 parts of 1,2-propylene glycol, 50-100 parts of glycerine, 0.001-0.008 part of sodium fluorescein, 0.01-0.08 part of simethicone, 0.05-0.15 part of lanthanum chloride, 0.05-0.15 part of chelating agent and 0.1-0.5 part of silicate stabilizer. The engine coolant is high in stability, freezing resistance, rust resistance and scaling resistance, capable of avoiding pipeline blocking, effectively preventing corrosion to ferrous metal, tin, copper and copper alloy, aluminum and aluminum alloy, overcoming the technical defect of traditional water-containing cooling liquid that boiling occurs easily, facilitating full-load and high-load operation of an engine and ensuring that a vehicle can travel safely in severe environments such as highlands, deserts and cold areas, and especially suitable for military vehicles, high-end vehicles and high-power heavy-load trucks and passenger cars.