The invention relates to a comfortable fire resistant fiber and a preparation method thereof. The preparation method comprises the steps of blending a cellulose or acrylonitrile copolymer and an inherent flame retardant macromolecule according to the proportion, dissolving in a solvent to prepare a spinning solution, adopting a high-power spray head for stretching through controlling the viscosity ratio of a blend material, and obtaining the blend fiber with a fiber surface layer rich with inherent flame retardant macromolecules. The limit oxygen index of the blend fiber is 27 to 32 percent, the fire self-extinguish time is less than or equal to 5s, the equilibrium moisture regain is 8 to 15 percent, the breaking strength is 2.6 to 5.5cN/dtex, and the content of the inherent flame retardant macromolecule in the blend fiber is 5 to 18 weight percent. According to the comfortable fire resistant fiber and the preparation method thereof provided by the invention, a two-phase type in the blend fiber can be effectively adjusted, a flame retardant property of the blend fiber is improved, the content of the inherent flame retardant fiber is reduced, and the preparation method has the characteristics of simple process and low cost, and has an important significance on developing the eco-friendly comfortable fire resistant fiber with low cost.