In this study, first, β‐mannanase gene man derived from Bacillus amyloliquefaciens CGMCC1.857 was cloned and expressed in Bacillus subtilis 168 to generate B. subtilis M1. However, the extracellular β‐mannanase activity of B. subtilis M1 was not very high. To further increase extracellular β‐mannanase extracytoplasmic molecular chaperone, PrsA lipoprotein was tandem expressed with man gene in B. subtilis 168 to yield B. subtilis M2. The secretion of β‐mannanase of B. subtilis M2 was enhanced by 15.4%, compared with the control B. subtilis M1. Subsequently, process optimization strategies were also developed to enhance β‐mannanase production by B. subtilis 168 M2. It was noted that the optimal temperature for β‐mannanase production (25°C) was different from the optimal growth temperature (37°C) for B. subtilis. Based on these findings, a two‐stage temperature control strategy was proposed where the bacterial culture was maintained at 37°C for the first 12 h to obtain a high rate of cell growth, followed by lowering the temperature to 25°C to enhance β‐mannanase production. Using this strategy, the extracellular β‐mannanase activity reached 5016 ± 167 U/ml at about 36 h, which was 19.1% greater than the best result obtained using a constant temperature (25°C). The result of this study showed that PrsA lipoprotein overexpression and two‐stage temperature control strategy were more efficient for β‐mannanase fermentation in B. subtilis.