[Objective] We optimize the growth conditions of Bacillus subtilis BE-91 and its shake flask fermentation conditions producing extracellular β-mannanase. [Methods] Single-factor experiments were used to optimize the main factors (such as carbon source, nitrogen source, pH, temperature and so on) affecting the growth of B. subtilis BE-91 and its extracellular β-mannanase production in shake flask fermentation. Based on one-factor-at-a-time experiment, orthogonal tests were applied to obtain the optimal combination. [Results] The optimum growth conditions of B. subtilis BE-91 showed as follows: 0.3% beef extract, 0.2% yeast extract, 0.1% glucose, 0.4% konjac powder, 0.5% NaCl，initial pH of 6.0, and culture temperature of 35 °C. The optimum conditions for extracellular β-mannanase production were as follows: 0.7% konjac power, 0.4% soybean peptone, 0.1% (NH4)2SO4, 0.5% NaCl，initial pH of 6.0 and fermentation temperature of 35 °C. Under the optimized conditions, the highest extracellular β-mannanase production of B. subtilis BE-91 was 432.4 IU/mL in 10 h. Its extracellular β-mannanase production was more than 5-fold higher than that from other relevant strains reported, and the time appeared 14?86 h shorter than others. [Conclusion] B. subtilis BE-91 has advantage in short cultivation time and high extracellular production of β-mannanase, so it is the specious resources with potential use in the enzyme preparation industry.