Natural polysaccharides regulate gut microbiota to promote host health and have garnered considerable attention in recent years. Prevotella copri, a common species within the genus Prevotella of the gut microbiota, is closely associated with human health. To investigate the differential enrichment effects of xylan, xyloglucan, arabinan, arabinoxylan, and arabinogalactan (used as sole carbon sources) on P. copri, single-strain and in vitro fermentation experiments were conducted. Parameters, including OD600, short-chain fatty acid content, and P. copri abundance were systematically evaluated. In single-strain fermentation, the growth of P. copri 2-27 and its acetic acid production were markedly enhanced by xylan and arabinan, with OD600 increases of 0.64 and 0.61, and acetic acid concentrations of 10.66 mg/mL and 9.87 mg/mL, respectively. During in vitro fermentation, arabinan exhibited the strongest enrichment capacity for P. copri (absolute abundance: 60.63 ng/mL), followed by xylan, arabinogalactan, and arabinoxylan. Notably, the arabinan group exhibited the highest production levels of acetic acid and butyric acid (4.60 mg/mL and 2.78 mg/mL, respectively). Although xylan was efficiently utilized, its enrichment effect on P. copri remained limited (6.98 ng/mL). Consequently, arabinan was identified as the most effective polysaccharide for promoting P. copri growth and enrichment. These findings provide a theoretical foundation for further exploration of polysaccharide–P. copri interaction and their implications for host health.