NOVELTY - Preparing beta -artemether, comprises e.g. dissolving artemisinin in methanol, ethanol, tetrahydrofuran or dimethylformamide, cooling, adding reducing agent sodium borohydride or potassium borohydride into artemisinin solution, reacting, filtering, vacuum extracting and concentrating, devitrifying, washing and drying to obtain dihydroartemisinin, reacting p-toluenesulfonic acid and dihydroartemisinin with e.g. methanol or ethanol, filtering and drying to obtain artemether crude product, and heating artemether crude product with e.g. methanol, cooling, filtering, washing, and drying.    USE - The method is useful for preparing beta -artemether.    ADVANTAGE - The method is mild, environment-friendly and is suitable for the commercial process; and has a product yield of more than 90% and purity of 99.2%.    DETAILED DESCRIPTION - Preparing beta -artemether, comprises: (a) dissolving artemisinin in absolute methanol, absolute ethanol, tetrahydrofuran or dimethylformamide organic solvent, cooling to 0-5 degrees C, adding reducing agent sodium borohydride or potassium borohydride into artemisinin solution, where the weight ratio of artemisinin to reducing agent is 1:(0.15-0.3), insulating and reacting for 1.8-2.5 hours, filtering, vacuum extracting and concentrating the filtrate until it is one ninth to one tenth of the original volume, adding water and processing devitrification, filtering, washing the filter cake to neutral with purified water, oven drying the filter cake at 40-60 degrees C to the constant weight, and obtaining the dihydroartemisinin; (b) adding one third of p-toluenesulfonic acid into the absolute methanol, absolute ethanol, ethylene glycol or isopropanol, adding dihydroartemisinin obtained in the step (a) under the state of stirring, reacting for 0.8-1.5 hours under room temperature, after dissolving the material, adding one third of p-toluenesulfonic acid, reacting for 1.8-2.5 hours under room temperature, after fully dissolving the material, adding the remaining p-toluenesulfonic acid, continuously reacting for 1.8-2.5 hours, where the weight ratio of p-toluenesulfonic acid to dihydroartemisinin is (0.05-0.1):1, adjusting the pH of the reaction liquid to neutral with alkali liquor, filtering, vacuum extracting and concentrating the filtrate to one fifth to one sixth of the original volume, cooling and processing devitrification, filtering, oven drying the obtained filter cake at 35-45 degrees C until the constant weight, and obtaining the artemether crude product; and (c) adding methanol, ethanol, ethylene glycol or isopropanol (2-4 folds of the weight of artemether crude product) into the obtained artemether crude product, heating at 35-45 degrees C, dissolving, cooling to room temperature under the condition of stirring, then cooling to 0-5 degrees C, processing devitrification for 3-5 hours, filtering, washing the obtained filter cake with freezing methanol, ethanol, ethylene glycol or isopropanol of 0-5 degrees C, where the weight of the washing liquid is 0.5-1 folds of the filter cake, oven drying at 35-45 degrees C until the weight is constant, and obtaining the product.