The invention discloses beta-1, 3-1, 4-dextranase gene and application thereof. The nucleotide sequence of the gene is shown in SEQ ID NO.1. The enzyme has the advantages that the germination of alternaria spores of pears and the extension of the germinal tube can be obviously controlled, and the damage action for the growth of hypha is achieved. Discovered by experiment of carrying out damaged inoculation on pear fruits and directly spraying recombinase and pathogenic bacteria, the diameter of diseased spots of the pear fruits inoculated with the recombinase is less than that of the diseased spots only inoculated with the pathogenic bacteria, and the decay degree is also obviously lower than that of the contrast; after the pear fruits are treated by enzyme liquid, the incidence is 37.61%, the disease prevention effect is 66.25%, and compared with the existing beta-1, 3-1, 4-dextranase, the preventing effect is better.