Abstract: In order to improve the efficiency of soybean meal fermentation in liquid state by Bacillus subtilis,the seed and fermentation culture were optimized. Through the single factor experiments to study the seed culture nitrogen sources,carbon sources,inorganic salts and temperature influence on biomass,it was concluded that the best seed culture was composed of 1% yeast extract,1% corn powder,1% KH₂PO₄ and 36 ℃ fermentation temperature. The biomass,neutral and alkaline protease activity was enhanced 210.10%,459.20% and 67.50%compared to conventional peptone medium. Then on this basis,by using orthogonal experiment to optimize the fermentation culture of carbon source quantity, inoculation size and temperature, the optimal fermentation conditions were 20% soybean meal,2% maize powder,1% KH2PO4,10% inoculation size and 36 ℃ culture temperature. The biomass, soluble protein and peptide content was 40. 90 %, 28. 60 % and 36. 40 % higher respectively,compared to the culture medium containing 22% soybean meal. The results showed that the optimized seed culture and fermentation culture could significantly improve the efficiency of the soybean meal liquid state fermentation by Bacillus subtilis.