Xylanase is the specific degradation enzyme of xylan, and can degrade xylan to oligosaccharides. Since livestock and poultry can not produce sufficient xylanase in alimentary tracts, the following effects can be achieved by adding exogenous xylanase to feeds: (1) Degrading xylans, thus efficiently decreasing chyme mucosity; (2) Enhancing chyme passing through intestinal tracts, thus increasing feed intake and production performance of livestock and poultry; (3) Enhancing the contact of chyme with digestive enzyme and intestinal mucosa, thus increasing digestibility and absorptivity of nutrients. (4) Breaking down the structure of cell walls and releasing the inside nutrients, thus increasing the utilization efficiency of feedstuff; (5) Increasing the activity of endogenous digestive enzymes, thus enhancing digestibility of animals; (6) Inhibiting growth of anaerobic microorganism colonies, thus reducing the incidence of intestinal diseases; (7) Enhancing the digestibility and utilization efficiency of feeds, and increasing proportions of wheat bran, wheat middlings and other plant feedstuff, thus reducing feed costs; (8) Enhancing absorption of nutrients, thus reducing environmental pollution.