This study aimed to enhance our understanding of the changes in the intestinal microbiota of juvenile largemouth bass (Micropterus salmoides) resulting from changes in dietary habits. The intestinal contents of 13-, 19-, 24-, and 46-day-old largemouth bass were continuously collected, representing the feeding live-bait period (LP), the first conversion diet period (CP1), the second conversion diet period (CP2), and the combination feed period (FP). 16S rRNA amplicon sequencing was used to investigate species diversity and differences in relative species abundance in the intestinal microbiota of juvenile largemouth bass. A Goods coverage value of 1 was obtained for the intestinal microbiota across all periods, suggesting that the sequencing results reflected the microorganisms present in the intestinal tract. The conversion of bait significantly affected the gut microbial diversity of the larvae and juveniles. Significant changes in species type were observed in the intestinal microbiota during CP1 and CP2, with the species composition being simpler. During LP and FP, the intestinal microbiota exhibited high evenness in species composition. The highest biodiversity and structural complexity in the intestinal microbiota were observed during FP, with 16 microbial communities having average relative abundances greater than 1% at the genus level. This number was only eight species for LP, and two or fewer species for both CP1 and CP2. Significantly higher average relative abundance values for Pseudomonas were observed in CP1 and CP2 (93.27% and 97.33%, respectively). Furthermore, significant differences in the relative abundance of dominant bacterial species were identified at different periods, indicating that diet conversion had a notable impact on gut-related functional microorganisms. This may be the intestinal response of largemouth bass to the absorption and utilization of feed, which has complex ingredients. This study provides preliminary data for the study of fish domestication and diet conversion and offers new insights into improving or optimizing largemouth bass feeding technology from the perspective of gut microbiota regulation.