The invention relates to a novel biological seed coating agent. The biological seed coating agent comprises components in parts by weight as follows: 15-30 parts of bacterial powder and 70-85 parts of a seed coating agent aid, wherein the bacterial powder comprises bacillus mucilaginosus, bacillus amyloliquefaciens and bacillus laterosporus in the weight part ratio of (1-3):(2-4):(2-4); the seed coating agent aid comprises components in parts by weight as follows: 40-60 parts of humic acid, 0.5-5 parts of Pulullan, 15-30 parts of polyvinyl alcohol, 0.05-1 part of a surfactant and 0.1-0.5 parts of a vigilant dye. The novel biological seed coating agent has good film-forming and slow-release functions, has higher film-forming strength, water-absorbing and water-resistant performance and chemical stability, has good biocompatibility with plants and cannot affect the germination rate of seeds; the seed coating agent prepared from bacterial powder of the bacillus mucilaginosus, the bacillus amyloliquefaciens and the bacillus laterosporus has effects of preventing and treating crop diseases and insect damage and promoting plant growth.