The invention discloses a feed additive capable of reducing aggressivity of mixed groups of pigs. The feed additive is prepared from raw materials in parts by weight as follows: 9-20 parts of Chinese thorowax roots, 7-15 parts of nutgrass galingale rhizomes, 8-15 parts of rhizoma chuanxiong, 4-10 parts of bitter orange stir-fried with bran, 7-16 parts of red peony roots, 8-18 parts of dried orange peel stir-fried vinegar, 4-10 parts of radix glycyrrhizae preparata, 5-12 parts of mint, 6-15 parts of combined spicebush roots, 5-12 parts of hawthorn fruits, 1-5 parts of chrysanthemums, 3-12 parts of cape jasmine, 3-6 parts of szechwan Chinaberry fruits, 5-10 parts of baical skullcap roots, 2-4 parts of L-tryptophan and 0.5-1 part of vitamin B. The invention further discloses a preparation method. The feed additive can sooth the liver, regulate qi and promote blood circulation to relieve pain, has a good regulation function on tension guard, emotion depression, irritability and bellicosity caused by pig group mixing under different production demands, the number of injured and dead pigs due to mutual fight of the pig groups is effectively reduced, the occurrence rate of tail baiting behavior, allotriophagia and other bad behaviors is reduced, few side effects are caused, the preparation cost is lower, and the feed additive is suitable for popularization and application.