The invention provides a preparation method of a microbial fermented prawn feed. The method comprises the following steps: step 1, mixing freshwater mussels, river snails and silkworm chrysalises, adding water, grinding the obtained mixture into slurry, adding pepsin and papain and carrying out enzymolysis so as to obtain first filter residues and supernatant; step 2, mixing lightyellow sophora roots, crofton weeds, garden columbine, leaves of oriental blueberry and herba corydalis, and conducting heating, refluxing and separation to obtain second filter residues and a filtrate; step 3, inoculating a primary culture medium with bifidobacterium bifidum, lactobacillus and bacillus natto and carrying out culturing; step 4, mixing corn meal, the first filter residues, the second filter residues, the filtrate, bacillus subtilis and clostridium butyricum, and conducting fermentation to obtain a first fermented product; mixing the first fermented product with clam shell powder, and conductingfermentation, filtration and drying to obtain a second fermented product; and step 5, mixing the second fermented product, compound vitamins and a powder, and conducting granulation. The prawn feed of the invention contains probiotics which can increase the immune system functions of the prawns, and can also treat intestinal flora disorder, improve intestinal environment, and promote intestinal patency.