The invention relates to a feed additive for increasing dorsal muscle thickness of fancy carp. The feed additive comprises the following components by weight percent: 10-20% of powdered milk, 8-15% of whole egg powder, 10-20% of coating methionine, 5-10% of threonine, 8-15% of yam, 10-20% of red dates, 8-15% of semen kernel, 1-3% of schisandra chinensis, 1-3% of ginseng, 1-5% of poria cocos, 3-5% of almond, 1-5% of Gorgon fruit, 1-5% of semen coicis, 1-5% of lotus root starch, 0.1-0.5% of complex enzyme preparation and 0.1-0.5% of emulsifying agent. The feed additive can comprehensively enhance the spleen and stomach functions of the fancy carp, can promote digestion, can enhance the intestinal tract absorbing function and can effectively tonify qi, promote granulation, nourish vitality and tonify speech, help digestion and invigorate stomach; the feed additive is beneficial to reinforcement of fat metabolism, reduction of accumulated fat in intestinal tract and enterocoelia, reduction of liver burden and health maintenance of the fancy carp; the feed additive can improve the amino acid balance of the feed, can increase the ratio of methionine to lysine and threonine to lysine in the feed, can cause nutritional ingredients to be more beneficial to the deposition of muscle protein, can promote the dorsal muscle accumulation and can help the fancy carp to quickly grow 'two-layer muscle' and achieve higher ornamental value.