The invention discloses a method for preparing
xylooligosaccharide from a
biomass raw material and application of the
xylooligosaccharide to preparation of a
feed additive, and the preparation method comprises the following steps: removing impurities from the
biomass raw material containing lignocellulose, crushing, adding water, uniformly mixing, adding into a high-pressure reaction kettle, carrying out subcritical hydrothermal
hydrolysis reaction at 170-220 DEG C under the condition of homogeneous stirring, filtering, washing, and
drying to obtain the
xylooligosaccharide. And after the reaction is finished, rapidly cooling to normal temperature, carrying out
solid-liquid separation, collecting a
hydrolysis mixed solution, and finally, carrying out post-treatment. The preparation of the xylooligosaccharide can be completed through a one-step subcritical hydrothermal
hydrolysis reaction, and the particle size of the crushed
biomass raw material and the subcritical hydrothermal hydrolysis
reaction conditions are synergistically optimized, so that the yield of the xylooligosaccharide can be remarkably improved, and the generation of byproducts can be effectively reduced; the prepared xylooligosaccharide is rich in
polysaccharide active ingredients, so that the utilization of the feed by animals can be effectively promoted; in the preparation process, the use of auxiliary materials such as
maltodextrin,
corn starch and beta-
cyclodextrin is avoided, and the production cost can be remarkably reduced.