NOVELTY - Enzymatic purifying tussah pupae skin chitosan comprises washing to white film object, absorbing water, oven drying at 60 degrees C for 4 hours to constant weight, crushing, sieving through 60 mesh to obtain powder, adding 10-15% citric acid according to solid liquid ratio of 1:10, desalting at 80 degrees C for 2-3 hours, water washing to neutral, repeating for 2-3 times, removing powder inorganic salt, selecting alkaline protease at enzyme substrate ratio of 3000-4000 u/g, regulating pH, hydrolyzing for 6-8 hours, filtering slag, water washing to neutral, and oven drying to constant weight.    USE - Method for enzymatic purifying tussah pupae skin chitosan (claimed).    ADVANTAGE - The product is easy to collect and process, and has uniform structure and high molecular weight. The method is scientific and reasonable, has short production period, simple technique and less wastewater and waste liquid, and does not destroy and pollute environment.    DETAILED DESCRIPTION - Enzymatic purifying tussah pupae skin chitosan comprises:    (A) washing to white film object, absorbing water, oven drying at 60 degrees C for 4 hours to constant weight, crushing, sieving through 60 mesh to obtain powder, adding 10-15% citric acid according to solid liquid ratio of 1:10, desalting at 80 degrees C for 2-3 hours, water washing to neutral, repeating for 2-3 times, removing powder inorganic salt, selecting alkaline protease at enzyme substrate ratio of 3000-4000 u/g, regulating pH at 60-65 degrees C to 8, hydrolyzing for 6-8 hours, filtering slag, water washing to neutral, and oven drying to 60 degrees C for 4 hours to constant weight;    (B) immersing into 1% hydrogen peroxide solution according to solid liquid ratio of 1:10, oxidation decoloring at 80 degrees C for 2 hours, filtering liquid, water washing to neutral, oven drying to 60 degrees C for 4 hours to constant weight to obtain light yellow powder shape chitosan, adding 55% sodium hydroxide solution according to material liquid ratio of 1:20, keeping at 90 degrees C for 15 hours, and removing chitin acetyl to obtain coarse chitosan; and    (C) adding 10% acetic acid solution to dissolve, standing for 24 hours, centrifuging at speed of 3000 revolutions/minute (rpm), removing impurities, taking supernatant, adjusting pH with 1 N sodium hydroxide solution to 10, isoelectric sedimenting, centrifuging at speed of 3000 rpm, collecting precipitate, adding deionized water, forming chitosan suspension to pH of 7.0, centrifuging at speed of 3000 rpm, collecting precipitate, washing with 95% ethanol, and drying to obtain high purity light yellow crystal shape.