NOVELTY - Extracting erythritol from erythritol mother liquor comprises (a) concentrating dry matter of erythritol content, standing and precipitating the concentrated erythitol content into evaporator and then concentrating erythritol sugar paste and (b) taking erythritol sugar alcohol bone and alcohol erythritol crystal as seed crystal, adding erythritol sugar paste to seed crystal, adding anhydrous ethanol with the erythritol sugar paste and then stirring and heat preservating, cooling the obtained product to room temperature and then freezing and crystallizing to form crystalline of massecuite.    USE - The method is useful for extracting erythritol from erythritol mother liquor (claimed).    ADVANTAGE - The method simply and economically extracts erythritol from erythritol mother liquor with high purity, crystal content (more than 99.5%) and yield rate (10%), low energy consumption and improved quality in an eco-friendly manner.    DETAILED DESCRIPTION - Extracting erythritol from erythritol mother liquor comprises (a) concentrating dry matter of erythritol content (40-55 %) to 40-65%, standing and precipitating the concentrated erythitol content for 3 days into an evaporator at temperature of 75 degrees C and vacuum degree of 0.09 MPa and then concentrating erythritol sugar paste (70-75 %), (b) taking erythritol sugar alcohol bone (0.05-2 %) and alcohol erythritol crystal as seed crystal, adding erythritol sugar paste to the seed crystal with erythritol content greater than 99.5% and fineness of 200 meshes, adding anhydrous ethanol (1-7 vol.%) with the erythritol sugar paste and then uniformly stirring and heat preservating at 68 degrees C for 3 hours, naturally cooling the obtained product to room temperature and then freezing and crystallizing at 5 degrees C for 10-15 hours to form crystalline of massecuite, (c) centrifuging crystalline of massecuite at low temperature and then bi-alcohol leaching to obtain primary erythritol without water, (d) adding deionized water with primary erythritol to dissolve and dry, decoloring the primary erythritol (30-35 %) by active carbon at 40-75 degrees C for 60-120 minutes and then filtering and separating to obtain destaining solution, performing ion exchange of the destaining solution by D301 anion exchange resin, -001X7 cation exchange resin and -D301 anion exchange resin, refining and purifying the erythritol material liquid with ion exchange rate more than 99.8 % and conductivity less than 10 mu .second/cm, (e) evaporating and concentrating the erythritol material liquid to dry at mass percentage of 70-75, cooling the dried product at 0.5-5 degrees C/hour to obtain the crystallized sugar paste and (f) centrifuging and drying the crystallized sugar paste.