As research into the relationship between the gut microbiome and health continues to evolve, probiotics are garnering increasing interest among consumers. Fermentation is recognized as an efficacious biotechnology for augmenting the nutritional and functional attributes of foods. In this study, the ameliorative effects of Lycium barbarum L. lyophilized powder fermented with Lactiplantibacillus plantarum NXU0011 (LP+Ly) on dextran sodium sulfate (DSS)-induced ulcerative colitis (UC) in mice were investigated employing immunohistochemistry, qRT-PCR, macrogenomics, and metabolomics. The results revealed that LP+Ly intervention significantly ameliorated histopathological inflammation in the ulcerated colon, diminished the expression of inflammatory markers such as IL-6, P-STAT3, and miR-214, and enhanced the diversity of intestinal flora in the mouse model group. Moreover, there was an increase in the abundance of beneficial bacteria, including Lactobacillus, Prevotella, and Akkermansia. Metabolomic analysis indicated that 15 metabolites, including citrulline, D-xylose, and alpha-ketoisovaleric acid, exhibited significant variations following the LP+Ly intervention. The metabolic pathways that displayed substantial differences included tryptophan biosynthesis, arginine biosynthesis, and amino sugar and nucleotide sugar metabolism. LP+Ly effectively improved the inflammatory state within the intestines by modulating arginine biosynthesis, thus alleviating the impact of UC.