Abstract: The wastewater from soybean processing（yellow serofluid）was used to optimize the fermentation medium condition of antagonistic bacterium Pb-4 against fusarium wilt. The single factor experiments were conducted to screen the carbon source of Pb-4 strain in yellow serofluid medium. Orthogonal experiments L₁₈（3⁵）were designed to select the optimal carbon source and inorganic components for Pb-4 strain in yellow serofluid medium，and determine the optimal fermentation medium formulation. The fermentation temperature，pH and inoculation amount of Pb-4 strain were optimized by response surface method（RSM）. As results，the composition of the optimal medium was yellow serofluid 1 000 mL，corn flour as the optimal carbon source 30 g，（NH₄）₂SO₄ 2 g，MgSO₄ 1.5 g，CaCO₃ 1.5 g and FeSO₄ 0.3 g. The fermentation conditions after optimization were as：temperature 36.3℃，inoculum size 5%，pH 7.4 and incubation time 40 h. Under the optimized conditions，the number of fermented bacteria was up to 42.8×10⁸ CFU/mL_，and the maximum biomass OD₆₆₀ was 0.393，which was in accord with the predicted value 0.390. In conclusion，the optimized medium can be as an effective substitute for traditional medium like peptone，yeast powder，glucose，etc.，moreover as it is simple，cost-efficient and environmentally friendly，thus it can be used as raw material for the scale production of microbial agents.

Key words: yellow serofluid, Bacillus amyloliquefaciens, Fusarium oxysporum f. sp. lycopersiici, antagonistic bacteria, fermentation condition optimization