The invention provides a bacillus Bacillus sp. strain and its application, and belongs to the technical field of microorganisms. The strain is preserved in the China General Microbiological Culture Collection Center (the short name is CGMCC) in March 7, 2017, and the address is No.3 institute of microbiology, Chinese academy of sciences, No.1 institution, Beichen west road, Chaoyang district, Beijing city. The strain is named as bacillus Bacillus sp., and the preservation number is 13725. The strain is separated out from salivary glands of parasitic insects, namely procecidochares utilis, of ageratina adenophora, biological infection can be quickly and efficiently conducted on the ageratina adenophora, the seed germination of ageratina adenophora can be significantly, and ageratina adenophora seedlings are thus diseased in the suitable environment. The strain can be used for preparing a fungicide using the strains as active ingredients or one of the active ingredients for preventing and controlling ageratina adenophora. The strain has a good application prospect in the field of ageratina adenophora prevention and control.