The invention relates to the field of microbial fermentation, and in particular to a method for fermentation production of beta-mannase. The method comprises the step of expressing beta-mannase by aspergillus usamii By247 through fermentation. According to the mannose produced by the invention, palm meal is used as one of the fermenting materials, and animal experimental results show that the mannase can decompose antinutritional factors in the palm meal in unconventional feed well and remarkably improve the production performance of animals. The temperature resistance, the feed and material decomposing capacity of the mannase and the result of animal experiments are better than those of other merchant beta-mannase.