A method for manufacturing composite fiber of hemp includes steps of: preparing hemp material: cutting stem of hemp into pieces, drying and charring the pieces of hemp at 800 to 1200 degrees Celsius and grinding the pieces of hemp into powder to form a hemp material; preparing primary granule: mixing the hemp material and nylon granules in a weight ratio of 5-20:95-80, melting and granulating the hemp material and nylon granules to form primary granules; preparing mixed granules: mixing and melting the primary granules and nylon granules in a weight ratio of 5-20:95-80 and granulating to form mixed granules; spinning: melting the mixed granules to spin into a composite fiber.