The invention discloses a dietetic food composition for losing weight. The composition comprises the following ingredients: fresh meat and aquatic product, vegetables, fruits, dried mushroom products, cereals, beans, nut meat, edible vegetable oil, eggs, protein hydrolysate powder, dietary fiber powder, konjac powder, guar gum, polyols, phosphatidylcholine, fruit polyphenols, L-carnitine, vitamin A, vitamin E, vitamin C, thiamine hydrochloride, riboflavin, nicotinamide, pyridoxine hydrochloride, folic acid, cyanide-containing cobalt and pantothenic acid. By adopting the dietetic food composition disclosed by the invention, the total energy intake is reduced under the premise of ensuring normal basic metabolic rate, the requirements of the body on protein at a low-energy diet period are improved, and related nutrients are replenished to facilitate body fat, visceral fat and blood lipid metabolism, so as to achieve the target of losing weight. Meanwhile, the invention also discloses a preparation method of the dietetic food composition and use of the dietetic food composition in preparation of a medicament for preventing or treating an obesity disease.