The invention discloses a bacillus gene knockdown carrier plasmid pBD1 based on dCas9, construction and application. The plasmid pBD1 is constructed by utilizing multiple molecular biology methods such as PCR, enzyme digestion, enzyme linking, sequencing and transformation, the plasmid pHY300-dCas9-sgRNA (pBD1) containing IPTG an inducible Pgrac promoter, dCas9 and sgRNA is constructed on the basis of bacillus expression vector, and the plasmid is theoretically suitable for a broad bacillus range because of having a large promoter strength and a wide host range.