Polysaccharides from Fuzhuan brick tea (FBTPS), one of most important bioactive components in tea, showed various health-promoting functions. Our previous work demonstrated that the crude FBTPS (CFBTPS) could modulate the gut microbiota. However, which purified fraction in CFBTPS contributing to the modulation of gut microbiota remains unclear. Thus, the fermentation characteristics and probiotic activity of a purified fraction (FBTPS-2-1) of CFBTPS were evaluated in this work. The results showed that gut microbiota could utilize FBTPS-2-1 to produce short-chain fatty acids including acetic, propionic, n-butyric and n-valeric acids. FBTPS-2-1 could modulate the structure and metabolic pathways of gut microbiota. FBTPS-2-1 could increase the health-promoting gut microbiota such as Prevotellaceae and Bifidobacteriaceae, and decreased the harmful bacteria such as Enterobacteriaceae and Fusobacteriaceae. The results of metagenomics showed that Prevotella copri and Megamonas funiformis were the dominant bacteria after fermentation of FBTPS-2-1. Furthermore, FBTPS-2-1 could regulate the biosynthesis and metabolism pathways of gut microbiota. Thus, the enrichment of food with FBTPS-2-1 is expected as a potential strategy for promoting human health due to modulation of gut microbiota.