NOVELTY - 1-deoxynojirimycin is prepared by crushing dried mulberry to obtain 20-40 mesh powder, adding water with amount of 6-10 times weight of powder, heating at 40-50 degrees C, adding 0.05-0.2 wt.% enzyme compound, hydrolyzing for 3-5 hours, filtering to obtain filter residue, extracting with hydrophilic solvent at 70-90 degrees C in extraction device for 3-4 times in which amount of hydrophilic solvent is 6-9 times weight of filter residue, extraction time is 1.8-2.2 hours, and hydrophilic solvent is hydrophilic solvent containing 0.2-0.4 vol.% acidic solution, combining extracts, and drying.    USE - Preparation of 1-deoxynojirimycin (claimed).    ADVANTAGE - Preparation process is simple, safe, environment-friendly, and suitable for industrial production, does not contain organic solvent which is harmful to human, and has low production cost, reduced energy consumption, and increased extraction efficiency.    DETAILED DESCRIPTION - 1-deoxynojirimycin is prepared by crushing dried mulberry to obtain 20-40 mesh powder, adding water with amount of 6-10 times weight of powder, heating at 40-50 degrees C, adding 0.05-0.2 wt.% enzyme compound, hydrolyzing for 3-5 hours, filtering to obtain filter residue, extracting with hydrophilic solvent at 70-90 degrees C in extraction device for 3-4 times in which amount of hydrophilic solvent is 6-9 times weight of filter residue, extraction time is 1.8-2.2 hours, and hydrophilic solvent is hydrophilic solvent containing 0.2-0.4 vol.% acidic solution, combining extracts, drying, filtering, concentrating under reduced pressure until volume is 1/3- one half , cooling at 20-30 degrees C, adjusting pH to 8-9 using 1-2 mass% alkaline solution, adding alcohol with amount of 3-4 times of said mixture to adjust pH, stirring for 10-15 minutes, standing for 3-4 hours, centrifuging in tube at 10000-14000 rpm to obtain centrifuged liquid, filtering in ultrafiltration membrane at room temperature with organic pore diameter of 5-10 kDa and pressure of 25-35 bar to obtain ultrafiltration permeate, filtering in nanofiltration membrane at room temperature with organic pore diameter of 300-800 Da and pressure of 0.5-1.5 MPa to obtain nanofiltration permeate, concentrating under reduced pressure until volume is one quarter -1/6 to obtain concentrate, and drying.