The invention aims to provide a method for producing beta-mannase by utilizing Aspergillus niger fermentation. According to the method, beta-mannase can be secreted and expressed by growing the Aspergillus niger in a liquid culture medium for 96 hours; the most preferable catalytic temperature of mannase is 40 DEG C, the most preferable pH value is between 2 and 6, the catalytic activity loss of mannase cannot exceed 40% after maintaining the temperature at 70 DEG C for 20 min, and mannase has a relatively good heat resisting property; and under a shake flask condition, the fermenting activity reaches at most 1200 U/mL, and mannase has a potential prospect to be used as a feed additive.