Abstract: The frozen fish is widely used in the culture of largemouth bass Micropterus salmoides. However, feeding of frozen trash fish not only lowered conversion rates but also caused the waste of natural resources and serious environment pollution. It is an inevitable trend for the largemouth bass aquaculture industry to replace frozen trash fish with formulated feed. In the present study, the frozen fish, formulated feed and frozen fish plus formulated feed (mixed) were used to investigate their effects on growth performance and intestinal bacterial community of M. salmoides. Results showed that the formulated feed group had the lowest average final body weight, body length, weight growth rate and specific growth rate, which were significantly lower than that of the frozen fish group and the mixed group (P<0.05), but there were no significant differences between the frozen fish group and the mixed group (P>0.05). The community richness of the intestinal microbiome was the highest in formulated feed group, and the lowest in frozen fish group. On the contrary, the diversity of the intestinal microbiome was the highest in frozen fish group, and the lowest in formulated feed group. Eight phyla including Firmicutes, Proteobacteria, Actinobacteriota, Cyanobacteria, Bacteroidota, Planctomycetota, Chloroflexi and Acidobacteriota were the dominant bacterial phyla. In the genera level, Mycoplasma, Klebsiella and Synechococcus_CC9902 were the dominant genera in the frozen fish group, while Klebsiella, Romboutsia and Mycobacterium, Mycoplasma, Candidatus_Brocadia and Romboutsia were the dominant genera in the formulated feed group and the mixed group respectively. Functional prediction showed that the abundance of functional genes involved in “energy production and conversion”“carbohydrate transport and metabolism”“amino acid transport and metabolism” and “lipid transport and metabolism” were dominant in the formulated feed group. Meanwhile, the abundance of functional genes involved in “nucleotide transport and metabolism”“coenzyme transport and metabolism” and “translation, ribosomal structure and biogenesis” were dominant in the frozen fish group. The results suggested that different diets significantly affected growth performance, the composition and functions of intestinal microflora. Furthermore, the present study provided scientific data for healthy cultivation and formulated feed innovation of M. salmoides.