The invention discloses a bacillus synergist and a synergistic biocontrol bacterium agent. The bacillus synergist is prepared from, by mass, 10%-80% of soybean pulp, 10%-80% of methylcellulose and 10%-80% of sucrose. According to the bacillus synergist, the soybean pulp, the methylcellulose and the sucrose are compounded, the bacillus synergist is used for a bacillus biocontrol bacterium agent, germination of spores of the bacillus can be promoted, and the survival rate of biocontrol bacteria is increased; the control effect of the biocontrol bacteria on disease bacteria is improved, the antagonistic action and negative effect of indigenous microorganisms on bacillus biocontrol bacteria are weakened, rapid germination and growth of the biocontrol bacteria are promoted, and the control effect of the biocontrol bacteria is improved; the synergistic effect of the bacillus synergist on the bacillus biocontrol bacterium agent is obvious through field experiments.