The invention discloses a method of producing a protein feed by a liquid-solid two-step fermentation method. The method comprises the following steps: performing liquid culture on corynebacterium glutamicum, candida utilis, bacillus subtilis, lactobacillus plantarum and aspergillus oryzae so as to obtain corynebacterium glutamicum fermentation liquor, candida utilis fermentation liquor, bacillus subtilis fermentation liquor, lactobacillus plantarum fermentation liquor and aspergillus oryzae fermentation liquor; mixing the corynebacterium glutamicum fermentation liquor, the candida utilis fermentation liquor, the bacillus subtilis fermentation liquor, the lactobacillus plantarum fermentation liquor and the aspergillus oryzae fermentation liquor so as to obtain mixed bacterium liquor; loading raw materials of soybean meal, cluster bean meal, cottonseed meal and the like into an explosion vat for performing steam explosion; after steam explosion, mixing materials, the mixed bacterium liquor and molasses in proportion, and adding an enzyme preparation so as to obtain mixed materials; conveying the mixed materials into a special modularized solid-state biological raw material continuous fermentation device for enzymolysis and fermentation, and drying the fermented materials so as to obtain the protein feed. According to the method disclosed by the invention, the modularized automatic fermentation device is adopted, the materials after explosion, the fermented bacterium liquor and the enzyme preparation are mixed, then the mixed materials are loaded into the automatic fermentation device for enzymolysis and biological fermentation, so that requirements for automatic temperature control, automatic dampness control and automatic ventilation control are met, the bioconversion rate is high, the fermentation period is short, the consumption is low, the cost is low, and mechanized and large-scale production requirements can be met.