Present invention involves a method for preparation of a feed additive containing surfactin, which uses a high-yield mutant strain, Bacillus subtilis T, and soybeans as the substrate in semi-solid state fermentation and after drying and grinding of the fermented soybeans into soybean powder to give a feed additive containing surfactin； wherein each kilogram of the fermented soybean powder contains about 6-7 g of surfactin. The invention found feed grouper with the feed additive containing surfactin can promote its growth rate, the expression of its immune genes is higher (e.g. AMP, Mx and IFN-induced protein), and the mortality rate of virus-infected fish is significantly lower, indicating the feed containing surfactin has the effects of growth promotion, immunity enhancement and provides resistance to pathogen infection.
