This study investigated the effects of dietary epigallocatechin gallate (EGCG) on rumen fermentation characteristics, and rumen microbiota in Hu sheep. Fifty-four healthy four-month-old male Hu sheep, with similar body weight, were randomly allocated to three groups (n = 18 per group): a control group (CON), and two experimental groups, L and H, which received a basal diet supplemented with 0, 300, or 1000 EGCG/head/day, respectively. The results showed that EGCG did not significantly affect ruminal pH, the concentrations of propionate, isobutyrate, isovalerate, and valerate, or the acetate to propionate ratio (P > 0.05). However, the ammonia nitrogen concentration was significantly lower (P < 0.05) in both the L and H groups, whereas the concentrations of acetate, butyrate and total volatile fatty acids were significantly increased (P < 0.05). EGCG had no effect on the alpha or beta diversity of rumen bacteria (P > 0.05). Among the dominant phyla, the relative abundance of Desulfobacterota was significantly higher (P < 0.05) in the L and H groups. For Verrucomicrobiota, a significant increase was observed only in the H group relative to both the CON and L groups (P < 0.05). At the genus level, the abundance of uncultured_rumen_bacterium was significantly increased (P < 0.05) in the H group. Correlation analysis revealed significant associations between rumen fermentation parameters and specific microbial taxa. Acetate and butyrate levels were positively correlated with several bacterial groups involved in carbohydrate fermentation. Dietary EGCG supplementation influenced the rumen microbial community, resulting in lower ammonia nitrogen and higher volatile fatty acid concentrations, thereby improving rumen fermentation efficiency in Hu sheep.