NOVELTY - Ailanthus seed polysaccharide preparation involves drying Ailanthus bark at 20-60 degrees C, and then crushing them to obtain 40 meshes size particle. The obtained material is extracted with water at 50-90 degrees C for 1-4 hours, where mass volume ratio of powder and water is 1:10-30. The obtained extract is filtered, and then extraction process is repeated. The obtained extracts are combined, and then filtered. The obtained filtrate is concentrated under reduced pressure. The obtained material is mixed with Sevag reagent with stirring for 20 minutes.    USE - Method for preparing Ailanthus seed polysaccharide for preventing and treating tobacco from tobacco mosaic virus (claimed).    ADVANTAGE - The method enables to prepare Ailanthus seed polysaccharide in simple, cost-effective and eco-friendly manner, and is safe for human and animal.    DETAILED DESCRIPTION - Ailanthus seed polysaccharide preparation involves drying Ailanthus bark at 20-60 degrees C, and then crushing them to obtain 40 meshes size particle. The obtained material is extracted with water at 50-90 degrees C for 1-4 hours, where mass volume ratio of powder and water is 1:10-30. The obtained extract is filtered, and then extraction process is repeated. The obtained extracts are combined, and then filtered. The obtained filtrate is concentrated under reduced pressure. The obtained material is mixed with Sevag reagent with stirring for 20 minutes, and then the obtained material is centrifuged at 5000 revolutions per minute for 10 minutes. The protein layer is removed from the obtained material, and then the process is repeated to remove protein. The obtained aqueous phase is dialyzed against distilled water for 36 hours, and then the obtained material is added with 2-5 times ethyl alcohol. The obtained material is performed for precipitation at -20 degrees C to 10 degrees C for 12-48 hours, and then the obtained material is centrifuged at 5000 revolutions per minute. The obtained precipitate is washed successively with ethanol, acetone and diethyl ether twice to remove impurity. The obtained material is dried at 30-70 degrees C, and then ground to obtain the finished product.