The invention discloses a composition for dietetic therapy, reducing weight and reducing blood lipid and a preparation method of the composition. The composition is prepared from the raw materials of duck blood, cordyceps militaris, ginseng, bitter gourds, navy beans, auxiliary materials and the like. The composition is prepared through the following technological processes of performing sterilization, drying, crushing and mixing on the raw materials, adding the auxiliary materials including edible starch, dextrin, xylitol, polyvidone K30 and the like, uniformly mixing the processed raw materials and the added auxiliary materials so as to obtain mixtures; granulating the mixtures so as to obtain granules; tabletting the granules so as to obtain tablets; and airing the tablets, selecting qualified tablets, and packaging the selected tablets so as to obtain tabletting foods containing the composition and used for dietetic therapy, reducing weight and reducing blood lipid. The composition disclosed by the invention is formed according to the scientific principle of reducing weight and reducing blood lipid, the catabolism of fat can be accelerated, and the effects of dietetic therapy, reducing weight and reducing blood lipid are achieved. Compared with conventional like products in the current market, the composition disclosed by the invention is safe to eat, free from dependence, not easy to generate the springback phenomenon, free from obvious toxic and side effects and beneficial to the health of bodies.