Abstract: In order to study the effects of combined application of Piriformospora indica and Bacillus subtilis Tpb55 on tobacco's resistance to bacterial wilt, a pot experiment was conducted using Yunyan 87 as the test material to analyze the control effects and mechanisms of the two biocontrol bacteria on tobacco bacterial wilt. The results showed that compared with the control, both P. indica and B. subtilis Tpb55 delayed the occurrence of tobacco bacterial wilt. Control efficiency of the combined application was 75.00%, which was significantly higher than those of single applications. The combined and single applications all raised the activity of superoxide dismutase(SOD), peroxidase(POD), catalase(CAT) and phenylalanine ammonia-lyase(PAL)in tobacco leaves, induced the expression of disease resistance genes PR2 and GST, enhanced the activities of sucrase, urease and acid phosphatase along with α diversity of bacterial communities in tobacco rhizosphere soil, and changed the structure of bacterial communities. The combined application thus yielded better results. After the combined application, the relative abundance of dominant microbial communities such as Chloroflexi, Actinobacteriaota, Acidobacteriota, Myxococcota at phylum level and SBR1031, A4bh, Chryseolinea and Vicinamibacteraceae at genus level in the tobacco rhizosphere soil was higher than that after the single applications. Both P. indica and B. subtilis Tpb55 enhanced the resistance of tobacco against bacterial wilt, and the combined application yielded better results than those of single applications, providing experimental basis for the biological control of tobacco bacterial wilt.