The invention relates to a preparing method of a barbecued horse mackerel fillet food. The preparing method comprises the steps: based on preferred horse mackerel raw materials, removing backstabs, removing heads, removing vertebrae, removing viscera, removing abdominal bones and fish bones of the raw material fishes, taking the fish bodies, and cutting into fish fillets; after cleaning the fish fillets, putting into a flavoring liquid for immersion to get tasty; controlling the liquid, placing in plates, and controlling the temperature for first roasting; taking out, coating a layer of a formulated oil on the surfaces of the fish fillets while the fish fillets are hot, carrying out second barbecue under a condition of high temperature, rapidly cooling, packaging, sterilizing, and thus obtaining the finished product, wherein the flavoring liquid is prepared by blending apple vinegar, table salt, monosodium glutamate, high fructose syrup, sorbitol, soy sauce, mirin, a fresh ginger juice, a skipjack extract, a lemon juice, a fermented glutinous rice juice and water according to a proportion, and the formulated oil is prepared by blending a salad oil, an onion oil and a peanut oil according to a proportion. The preparation method is reasonable in procedures, reasonable in ingredients and strong in operability; and the barbecued horse mackerel fillet food prepared by the method has the advantages of rich nutrition, crisp outside, tender inside, fresh and delicious taste and convenient eating.