The invention discloses a water-based antirust agent for surface treatment of a flame-retardant seeder. The water-based antirust agent is prepared from, by weight, 39-40 parts of phytic acid, 7-9 parts of polyaspartic acid, 10-12 parts of waste polystyrene foam plastic, 1-2 parts of rosin amine, 2-3 parts of petroleum barium sulfonate, 3-4 parts of aminotri-methylene phosphonic acid, 1.8-2.1 parts of inositol hexaphosphoric acid, 1.5-1.8 parts of 3-aminopropyltriethoxysilane, 5-7 parts of a honeysuckle extract, 2-3 parts of sericin powder, 2.4-2.7 parts of nano-magnesium hydroxide, 3.4-3.7 parts of polyethylene glycol, 4.4-4.7 parts of polyvinyl alcohol and the balance deionized water. According to the water-based antirust agent, the phytic acid and the polyaspartic acid serve as main ingredients, polyethylene glycol and polyvinyl alcohol serve as macromolecule film-forming agents, and the modified waste polystyrene foam plastic is added to serve as a waterproof additive. Meanwhile, the other additives are added, and the antirust agent prepared according to the optimized formula is good in antirust effect, strong in flame-retardant effect, low in production cost, low in viscosity and easy to coat.