The invention relates to a method for preparing ethanol from yam raw materials, which comprises the following steps: removing peels of the yam raw materials by using a yam peeling device; crushing the peeled yam raw material; mixing and enzymolyzing the crushed products and enzyme; fermenting the obtained enzymolysis products; separating the ethanol from the fermented products; performing solid-liquid separation on fermented waste liquid to obtain a filter cake and waste water; and performing waste water treatment on the obtained waste water, wherein the chemical oxygen demand value of the waste water obtained after separation is between 30,000 and 35,000 mg/L. the method provided by the invention can effectively improve the yield of the ethanol, obviously reduce the pressure for treating the waste water, make the treated waste water meet the requirement of the environment.