The invention discloses a brevibacterium, an application and a preparation method of fermentation liquid of the brevibacterium. The brevibacterium is a phytophthora nicotiana antagonistic strain, andis collected in China Center for Type Culture Collection (CCTCC) in Wuhan University, Wuhan, China, with a collection number of CCTCC NO (number): M2018003. The brevibacterium can effectively antagonize phytophthora nicotiana and further achieves an effect of preventing and treating a tobacco black shank.