Abstract: The purpose of this study is to evaluate the control effect of a biochar bioagent on tobacco black shank disease and reveal its combined biocontrol mechanism. Biochar bioagent was prepared by loading Bacillus amyloliquefaciens CAS02 on biochar carrier, and its loading effect was evaluated. Using the susceptible variety "Xiaohuangjin1025" as the test material, the prevention and control effects of different treatments of biochar bacteria on tobacco black shank disease were studied in an indoor pot experiment, and the relevant mechanism were analyzed from the perspective of soil chemical properties and microbial community structure. The results showed that:(1) Biochar could effectively support biocontrol bacteria CAS02 with a load of 25.31×10⁸ CFU/g, giving full play to the role of carrier. (2) The control effect of CAS02 on tobacco black shank disease decreased to 2.08% after 25 days of application, while the biochar bioagent was highly effective and sustained, and still maintained 43.75% relative control effect on the 25th day. (3) The application of biochar agent significantly changed the rhizosphere soil chemistry. Compared with CK, the content of available phosphorus in the rhizosphere soil under the BC-CAS02 treatment increased by 49.58%, while the content of available potassium decreased by 17.39%. (4) By comparing the amplicon sequencing in the 16 S V3-V4 region of each treatment, the biochar bioagent significantly changed the soil microflora structure, and the relative abundance of disease-inhibiting beneficial bacteria such as WCHB1-32, Ochrobactrum and Arthrobacter significantly increased at the genus level. In conclusion, biochar bioagent can effectively improve the control effect of tobacco black shank disease by improving rhizosphere soil chemistry and microbial community composition.