The invention discloses a preparation method of fermented feed for hairy crabs. The preparation method comprises the following steps: (1) preparation of fermentation liquid: heating water to 100 DEG C, adding brown sugar, then performing heating for 5 min, adding EM strains, table salt and urea when the temperature is reduced to 40 DEG C, performing closed fermenting for 2 days and controlling thefermenting temperature at 35-37 DEG C; (2) preparation of feed raw materials: mixing corn, soybeans, pumpkins, mineral salt and fish meal uniformly; and (3) preparation of the fermented feed: mixingthe fermentation liquid in the step (1) and the feed raw materials mixed in the step (2), performing sealing by using a transparent plastic thin film, and performing fermenting in a sunny place for 24h to obtain the fermented feed which can be fed. The preparation method disclosed by the invention is simple and easy, and adopts microbial fermentation to degrade plant fiber, sugar, plant alkaloid and the like in plant feed into small molecular substances, thereby improving the utilization ratio of the plant feed, effectively saving the cost and reducing the incidence rate of diseases in the hairy crabs.