Abstract: In this study, 3.5% DSS was used to construct an animal model of colonic inflammation in mice, in order to study the relieving effect of commercially available pasteurized fermented milk on colitis mice and the possible mechanism. The effect of pasteurized fermented milk was studied by evaluating the disease activity index (DAI) in mice, observing colon tissue structure by HE staining, analyzing intestinal short-chain fatty acid content by gas chromatography-mass spectrometry (GC/MS), detecting inflammatory factors in colon tissue by ELISA levels, measuring myeloperoxidase (MPO) content and using immunohistochemistry for tight junction protein expression. The results of the study showed that pasteurized fermented milk could reduce the disease activity index DAI, alleviate colon tissue damage, increase the content of acetic acid, isopropionic acid, valerate acid and total acid in the intestinal short-chain fatty acids of mice, reduce the secretion of anti-inflammatory cytokines tumor necrosis factor-α (TNF-α) and leukocyte-mediated interleukin-1β (IL-1β) in mice, and increase the anti-inflammatory cytokines interleukin-10 (IL-10) secretion and decrease MPO activity. Further research showed that pasteurized fermented milk could increase the expression of tight junction proteins in the mouse gut and enhance intestinal epithelial barrier function. Therefore, pasteurized fermented milk could not only alleviate the symptoms of intestinal inflammation in mice, but might play its role by regulating the body's immunity and strengthening the intestinal barrier.