The invention discloses a luminous plant fiber and a preparation method thereof, and belongs to the technical field of anti-counterfeiting fluorescent fibers. The preparation method comprises the following steps: impregnating the pretreated plant fiber in an organic fluorescent solution; and filtering and drying the taken impregnated plant fiber to obtain the luminous plant fiber, wherein the plant fiber comprises a native cellulose fiber, a regenerated cellulose fiber or a recycled fiber; in the organic fluorescent solution, a solute is an organic fluorescent substance, and a solvent is an organic solvent; the impregnation time lasts for 10-30 minutes; the drying mode is vacuum drying. The luminous plant fiber disclosed by the invention has an excellent fluorescence property and processability.