The invention provides a brevibacillus brevis liquid-submerged fermentation method, and further provides a preparation method of a brevibacillus brevis wettable powder. The brevibacillus brevis liquid-submerged fermentation method comprises the steps: brevibacillus brevis seed liquid is inoculated into a fermentation culture medium with the volume ratio of the inoculation amount being 1-5% to be fermented till bacteria of 90% or above in obtained fermentation liquid are germs in form; the preparation method comprises the steps: the fermentation liquid is centrifuged to obtain concentrated bacterial liquid, then talcum powder, sucrose, maltodextrin and the concentrated bacterial liquid are evenly mixed and then spray-dried, a dry bacterium powder is obtained, sodium dodecyl benzene sulfonate, organosilicone, ascorbic acid and the dry bacterium powder are evenly mixed, then smashed under 30-50 DEG C, and pass through a 400-mesh sieve, and then the wettable powder is obtained. The methodis simple in process, the prepared biocontrol brevibacillus brevis wettable powder has a good control effect on tobacco black shank, safety and high efficiency are achieved, no residue and toxic and side effect exists, and using of chemical pesticides can be reduced.