Intumescent carbon layer thickness controllable type flame retardant and preparation method of flame-retardant wood

The invention belongs to the technical field of wood processing, and particularly relates to an intumescent carbon layer thickness controllable type flame retardant and a preparation method of flame-retardant wood, and the preparation method of the flame retardant comprises the following steps: putting phytic acid and urea into a reaction container, and heating, condensing and refluxing to obtain oily liquid; freezing the oily liquid in ultralow-temperature equipment; drying by using a freeze dryer to obtain a solid intermediate; and adding the solid intermediate, starch and glacial acetic acid into pure water, heating and stirring to obtain the required flame retardant. The raw material wood is coated with the flame retardant, and the flame-retardant wood can be prepared through drying in the shade, drying and water balance. According to the invention, phytic acid and urea are used as raw materials to obtain ammonium phytate with different reaction degrees; according to different proportions of phytic acid,