Abstract: To further clarify the inhibitory effect of Bacillus megaterium strain Bm on main tobacco diseases, the inhibiting effects of BM on tobacco mosaic virus(TMV), Phytophthora parasitica var. nicotianae and Ralstonia solanacearum were studied by the half-leaf, plate confrontation and inhibition zone methods, respectively. A strain with resistance to antibiotic was screened out with rifampicin, and its colonization laws in tobacco rhizosphere soil and on tobacco leaves were analyzed. Bio-control bacterium fermented broth was prepared and its field control effect was determined. The results showed that the inhibition rates of Bm fermented broth and its supernatant on TMV were 88.4% and 74.3% respectively, and the inhibition rate of the fermentation supernatant on the mycelia of Phytophthora parasitica var. nicotianae was 67.5% and the diameter of inhibition zone of Ralstonia solanacoarum in culture plate was 10.03 mm. There was no difference in growth traits between the resistant strain Bm-rifand the wild-type strain. The results of colonization experiments in greenhouse indicated that the population of stably colonized Bm-rif was 0.04×10⁵ cfu/g in soil without sterilization and 0.47×10⁵ cfu/g in sterilized soil, which were all significantly higher than those on tobacco leaves. Twenty-four hours before the TMV-GFP inoculation, the inhibition rate of foliage spray using the fermentation broth on primary infection of TMV was 44.04%. The field control effects of a diluted fermentation broth sprayed at the basal part of tobacco stalk against Phytophthora parasitica var. nicotianae and Ralstonia solanacearum were 68.09% and 51.02%, respectively. Therefore, Bm has antibacterial activity and can effectively colonize in tobacco rhizosphere soil, and has the potential to be an antibiological inoculant.