The invention discloses a preparation method of a mussel-imitated flame-retarding material. The preparation method comprises the following steps: preparing a solution; preparing magnesium hydroxide coated with first iron tannate; preparing magnesium hydroxide coated with second iron tannate; preparing magnesium hydroxide coated with third iron tannate; drying, mashing and granulating. According to the mussel-imitated flame-retarding material provided by the invention, a tannic acid-iron complex can be uniformly distributed on material surfaces, the wetting property of the material surfaces is improved, and a mutual effect of the material surfaces is promoted; meanwhile, iron salt has the effect of a smoke eliminating agent in the flame-retarding material; meanwhile, the material can also be cooperated with other flame-retarding materials, so that the flame-retarding effect of the material is improved.