The invention discloses fish soluble feed protein and a processing method thereof. The processing method comprises the following steps of: mixing fish soluble and bean pulp, adding a strain into the mixture for solid-state fermentation, directly mixing the obtained product without drying and other raw materials in a formula and taking the mixed products as a feed for pigs, birds and cattle, or drying and crushing the obtained product to prepare the fish soluble feed protein used for protein raw materials in the feed industry and breeding industry after the fermentation is finished. The method has the advantages of simple process, low equipment investment and low cost; and the fish soluble feed protein is strong in fragrance and good in food attraction, improves protein content, is high in small peptide content and easy to digest and absorb, eliminates anti-nutritional factor in the bean pulp, is rich in various beneficial functional nutrient components such as probiotic and the like, plays active roles in improving weight gain and feed conversion rate, strengthening the immune function of organisms, improving production performance and the like, can greatly replace fish meal in livestock and poultry feeds and aquatic feeds, remarkably reduce feed cost, turn the fish soluble into the value from the waste, and is favorable for environmental protection as well as energy conservation and synergism.