The invention belongs to the technical field of feed processing, and discloses a straw fermented feed and a preparation method thereof. The straw fermented feed comprises the following raw materials:green straw, traditional Chinese medicines, white carbon black, fumaric acid, montmorillonite powder, compound microorganisms and cellulase. The preparation method comprises the following steps: (1) harvesting the green straws, removing impurities, cutting the green straws into small sections with a length of 3-4 cm by using a chopping machine, and regulating moisture so as to obtain a silage rawmaterial; (2) respectively diluting the compound microorganisms and the cellulase with water, uniformly mixing the diluted compound microorganisms and cellulase with the silage raw material, loading an obtained mixture into a clean bag in a layered manner, treading and compacting the mixture once when the bag is filled with the mixture with a thickness of 25-35 cm, exhausting air, and tightening abag opening by using a rope; and (3) putting a material obtained in the step (2) into a fermentation tank for anaerobic fermentation, taking a fermented material out of the fermentation tank, addingthe white carbon black, the fumaric acid and the montmorillonite powder in proportion, and performing uniform mixing so as to obtain the straw feed. The straw feed disclosed by the invention takes thegreen straws and the Chinese herbal medicines as main raw materials, has the effects of strengthening the spleen and stomach, improving the appetite of livestock and enhancing the resistance of the livestock, and increases the weight of the livestock.