The present invention discloses one kind of prawn feed additive. The prawn feed additive is compounded with Chinese herbal medicine powder in 8-12 weight portions and solid lichen-forming bacillus material in 12-18 weight portions. The Chinese herbal medicine powder is prepared with isatis root, forthythia, astragalus root, agastache, Viola yedoensis and Chinese goldthread and through stoving and crushing. The solid lichen-forming bacillus material contains lichen-forming bacillus in 10<9> CFU/g. The prawn feed additive is added into prawn feed in the added amount of 0.15-0.50 wt% before the feed is pelletized into 1.5 mm size grains. By means of the synergistic effects of the Chinese medicine materials and the lichen-forming bacillus, the prawn feed additive has the functions of raising the activity of digestive enzyme, promoting the growth of prawn and raising the survival rate of prawn.