The invention belongs to the field of fiber materials and discloses a preparation method of a flame-retardant fiber material. The preparation method of the flame-retardant fiber material comprises the following steps: (1) heating 15-28 parts of polyurethane and 15-22 parts of chitin and performing melt blending on polyurethane and chitin in a high-speed mixing machine; (2) adding 6-12 parts of chlorinated polyethylene and 8-14 parts of polyarylether resin into a melt blending material, keeping the temperature constant and performing melt blending again; and (3) heating the melt blending material into a spinning solution, carrying out degassing treatment on the spinning solution, and after degassing, carrying out melt spinning, cooling, hot stretching and hot setting to prepare the flame-retardant fiber material.