The invention relates to a food fresh-keeping method, and discloses a tilapia fresh-keeping method, comprising a tilapia preservative, wherein the tilapia preservative is made of hydration sodium carbonate, sodium carbonate, sodium bicarbonate, hydration sodium citrate, sodium chloride, etc., and processed tilapia fillets are preserved under 0-4 DEG C after uniformly immersed for 10-15min in the tilapia preservative. The raw materials for preparing the tilapia preservative is in a foodstuff grade, is safe and innocuous, and accords with foodstuff security proposed by state at present. A shelf life of fresh tilapia flesh by using the preservative can reach 10-15 days, and sense, physical and chemical and microbe indexes of the tilapia flesh reach tilapia fillet requirement, and satisfies demands on fish flesh quality for consumers in our country. The tilapia flesh can obtain a long shelf life, it makes convenient for prolonging a circulation and shelf life of the fish flesh, and the raw materials have low cost.