To explore the effects of dietary seaweed polysaccharides (Algaevita 913) on the growth and intestinal health in fish, this study added 0‰, 1‰, 2‰ and 3‰ seaweed polysaccharides (D0–D3) to the commercial feed of largemouth bass (Micropterus salmoides) and set up a positive control with 2‰ yeast cell wall (D4). The five diets were used to feed the juvenile M. salmoides for 8 weeks. The results showed that the weight gain rate (WGR) and specific growth rate (SGR) in group D2 were the highest, which were significantly higher than those in the control group (D0) and D4 (P＜0.05). Moreover, the feed conversion ratio (FCR), hepatosomatic index, and viscerosomatic index were significantly lower in D2 than in D0 (P＜0.05). There was no significant difference in the whole fish body composition and digestive enzyme activity in the foregut of each group (P＞0.05). The integrity of the foregut villi in D2 and D3 was better than that in D0, and the thickness of the muscle layer and the number of goblet cells in D2 were significantly higher than those in D0 (P＜0.05). The lysozyme (LZM) activity in both D2 and D3 and catalase (CAT) activity in both D1 and D2 were significantly higher than those in D0 in the foregut (P＜0.05). The expression levels of zo-1, occludin, mucin-2, tlr4, hif, and il-10 mRNA in the foregut of fish in D2 and D3 were increased (P＜0.05), while the expression levels of il-1β and il-6 in D1–D4 and nf-kb mRNA in D2 significantly decreased (P＜0.05). The composition of short-chain fatty acids in the intestinal contents showed that the contents of isobutyric acid in D3 and acetic acid in D4 were significantly higher than those in D0 (P＜0.05). In terms of the intestinal microbiota structure, D0, D1, and D3 were clustered together, while D2 and D4 were highly similar based on the PCoA analysis. In D2 and D4, the abundance of Pseudomonas and Cetobacterium significantly decreased while the abundance of Ralstonia and Pantoea significantly increased (P＜0.05). The content of potential pathogenic bacteria in D1 was significantly lower than that in D0 (P＜0.05). The above results showed that adding 2‰ seaweed polysaccharides to the feed could improve the growth performance, intestinal villi integrity, intestinal immunity, antioxidant capacity, and improve the intestinal microbial structure, which was beneficial to intestinal health. For the WGR, SGR, and FCR, the optimum levels of seaweed polysaccharides in the feed of largemouth bass juveniles are 1.76‰, 1.77‰, and 1.74‰, respectively.