The invention discloses a method for fermenting alcohol by reusing alcohol grain liquid and medium-temperature anaerobic effluent. According to the process method, burdening liquid is added according to the feed liquid weight ratio of 1:1.5-2.4, the burdening liquid is composed of the alcohol grain liquid, the medium-temperature anaerobic effluent and supplemented clean water, the effluent is reused, and ammonium hydroxide or sulfuric acid are not required, so that the effluent treatment cost can be reduced. By controlling the feed water ratio and adjusting the proportion of alcohol grain liquid and the medium-temperature anaerobic effluent to control the pH value, the complex cost-increasing procedures of conducting acid radical removing, ammonia nitrogen removing and additionally adding of acid or alkali to adjust the pH value and the like on the medium-temperature anaerobic effluent in the traditional process are avoided, the production efficiency is greatly improved, the production cost is reduced, sewage discharge in alcohol production is greatly reduced, feed mixing water use cost and sewage treatment cost are saved, more additional products are produced, and considerable market economical benefit is brought.