The invention provides a method for producing beta-mannase by adopting lactic acid bacteria cultured by taking konjaku flour as the carbon source, relating to a method for producing beta-mannase by adopting lactic acid bacteria, for solving the problems that during the producing of mannase by adopting fungi in the prior art, the fermentation period is long, the bacteria for producing mannase has the potential biological safety hazards, and the activity of the lactic acid bacteria in producing the mannase is low. The method comprises the following steps: 1, inoculating lactobacillus plantarum to an MRS solid medium panel, and carrying out culturing; 2, picking single colonies, and carrying out culturing in MRS liquid medium; 3, carrying out centrifugalization, abandoning the supernatant, collecting thalli, and adjusting the cell concentration, thus obtaining the seed solution; 4, inoculating the seed solution to a fermentation medium, thus obtaining fermentation liquor; and 5, centrifugalizing the fermentation liquor, abandoning the thalli, and taking the supernatant, thus obtaining the mannase crude enzyme. The crude enzyme produced by adopting the method provided by the invention is high in enzyme activity, low in production cost, and short in production period, and the produced bacterial strain has no biological safety hazards. The method is applied to the field of microbial fermentation enzyme production.