The invention belongs to the technical field of aquaculture, and specifically discloses a feed additive for shrimps and a preparation method thereof. The feed additive for the shrimps is obtained by mixed fermentation of the following components by the mass percentage: 10-15% of photosynthetic bacteria, 20-30% of bacillus, 20-25% of yeast, 25-35% of lactic acid bacteria, 1-5% of brown sugar, 1-5%of rice bran, 0.5-1.0% of sea salt, and the balance auxiliary materials. The feed additive for the shrimps can play a role in protecting intestinal tracts of animals through microorganisms, improve the immunity of the shrimps, reduce the occurrence of diseases and improve the survival rate; the feed additive for the shrimps can improve the intestinal environment of the animals through microorganisms, increase the number of beneficial bacteria in the intestinal tracts, promote the digestion and absorption of a feed by the animals, reduce the food coefficient, promote the growth of the shrimps,improve the production performance, improves the density of shrimp seedlings, allows the shrimp meat to be fresh and sweet, have no fishy flavor and have complete shape, and can be widely used in thefield of aquaculture.