The invention belongs to the technical field of microorganisms, and in particular relates to a special multifunctional growth-promoting bacterium agent for soybeans, which is fermented from the FK19 strain, and the classification of the FK19 strain is named Bacillus megaterium (Bacillus megaterium), preserved on December 27, 2018 In China Center for Type Culture Collection, the deposit number is CCTCC M 2018925. The beneficial effects of the present invention are: the multifunctional growth-promoting bacterium agent of the present invention has obvious promoting effect on soybean growth, has obvious increasing effect on phosphorus content and potassium content of soybean leaves, and can increase soybean yield. Soybean roots will produce soybean lectin, which is a sugar-binding protein or glycoprotein of non-immune origin, which can be combined with polysaccharides of bacteria. The multifunctional growth-promoting bacteria agent of the present invention has soybean lectin affinity, and can Combined, adsorbed on the soybean roots, and then promote the synthesis of more isoflavones in soybeans, mediate the colonization of the bacterial strains in the soybean roots, so as to exert the growth-promoting function of the bacterial agent.