To explore the feeding effect of fermented formula feed in red swamp crayfish (Procambarus clarkii), unfermented and fermented feeds were fed to juvenile P. clarkii [initial body weight (4.91±0.18) g] in an indoor circulating water system for eight weeks. The effects of fermented feed on growth, muscle quality, digestion, antioxidant capacity, and intestinal flora structure of P. clarkii were analyzed. The results showed that, ① the dissolution rate of fermented feed was significantly lower than that of unfermented feed. ② The fermented diet significantly increased weight gain rate, and specific growth rate. Furthermore, it decreased feed conversion ratio, but had no significant effect on survival rate, hepatosomatic index (HSI), flesh content, and body composition. ③ The fermented diet significantly improved muscle hardness, elasticity, chewiness and stickiness of P. clarkii, and decreased adhesion. ④ The fermented diet significantly increased the activities of trypsin and lipase in hepatopancreas and intestinal tract, the activities of superoxide dismutase, acid phosphatase, and alkaline phosphatase in serum and hepatopancreas, and the total antioxidant capacity of the hepatopancreas. ⑤ The fermented feed significantly increased the length and width of intestinal villi. ⑥The fermented feed improved the intestinal microbial structure of P. clarkii, significantly increased the relative abundance of Firmicutes and Actinobacteria, and increased the diversity of intestinal flora. Overall, the fermented feed effectively improved the growth performance, muscle quality, digestion, and antioxidant capacity by improving the intestinal tract tissue structure and changing the structure of intestinal microorganisms of P. clarkii.