The invention discloses refined jute-kenaf fiber and a preparation method thereof. The fiber fineness of the jute-kenaf fiber is greater than 600 Nm, the fiber whiteness is greater than 50, and the strength is greater than 2.5 cN/dtex. In the degumming process of the preparation method disclosed by the invention, a method of combining bio-enzyme degumming with traditional chemical refining is adopted so as to further remove colloid from the jute-kenaf fiber and refine the jute-kenaf fiber without damaging the strength of the jute-kenaf fiber. The refined jute-kenaf fiber disclosed by the invention has the advantages of high fineness, high strength and good spinnability, and can be independently spun or blended with cotton, silk and other fibers to prepare top-grade products, thereby overcoming the defect that the jute-kenaf fiber cannot be applied to the field of top-grade products; and meanwhile, the antibacterial, humidity-absorbing and breathable functions of the product are increased, the varieties of the product are enriched, raw materials such as cotton, silk, chemical fiber and the like can be partially replaced, and the pressure on resource shortage is reduced.