Tibetan turnip (Brassica rapa L.) polysaccharide (TTP) is an active ingredient and has been studied for many years due to its biological effect. There are a few studies on its digestion properties and the regulation of the intestinal microbiota. In this study, the regulation of intestinal health by TTP was investigated in vitro and in vivo. The results showed that TTP was not degraded after simulated gastrointestinal digestion. When TTP was fermented by the gut microbiota, the content of short-chain fatty acids (SCFAs) and the relative abundance of Bifidobacterium, Catenibacterium increased; the relative abundance of Prevotella, Phascolarctobacterium decreased. The in vivo experiments showed that TTP could reduce the abundances of Muribaculaceae and enrich Lactobacillus. The results of KEGG indicated that TTP could promote arginine and ornithine metabolism, fructose and mannose metabolism, and lipopolysaccharide biosynthesis. These data showed that TTP exerted its prebiotic effect by regulating the intestinal flora and could be used for preventing disease and improving health by maintaining intestinal health.