ObjectiveTo investigate the effect and mechanism of modified Sini San in ameliorating intestinal mucosal barrier by observing its effects on short chain fatty acids （SCFAs） and high mobility group protein B1 （HMGB1）/receptor of advanced glycation end products （RAGE） signaling pathways in chronic stress rats. MethodsThe 50 male SD rats were randomly divided into control group，model group，low-dose modified Sini San group （7.34 g·kg^-1·d^-1），high-dose modified Sini San group （14.68 g·kg^-1·d^-1），and Fructo-oligosaccharides group （3.15 g·kg^-1·d^-1），with 10 rats in each group. Except for the control group，all other groups were subjected to chronic unpredictable stress/social isolation to create a chronic stress model for 6 weeks. After 4 weeks of modeling，each treatment group was given corresponding drugs by gavage for 2 weeks while modeling. The control group and model group were given the same volume of physiological saline. The effects of Modified Sini San on behaviors，body weight，Bristol score in feces and fecal moisture content in chronic stress rats were observed. Hematoxylin and eosin （HE） staining was used to observe the pathological changes in the cecum. The content of SCFAs in the cecal contents of rats were detected by Gas chromatography-mass spectrometry （GC-MS）. Immunohistochemistry and Western blot were used to detect the expression of HMGB1/RAGE pathway related proteins in cecal tissue. The levels of ZO-1，Occludin，and Claudin-1 in the cecal tissue were detected by enzyme linked immunosorbent assay （ELISA）. ResultsCompared with the model group，the sucrose preference rate，total distance traveled and the number of grid crossings in the open field test of rats in the low-dose modified Sini San group were obviously increased （P<0.05， P<0.01），and the immobility time in the open field test and the immobility time in the forced swimming test of rats in the low-dose and high-dose modified Sini San groups were obviously reduced （P<0.05， P<0.01）. Meanwhile，the Bristol score and fecal moisture content of rats in the low and high dose groups of modified Sini San were obviously increased （P<0.05）. The low-dose group of modified Sini San had intact mucosal layer structure in the cecal tissue and reduced infiltration of inflammatory cells. The content of SCFAs in the cecal contents increased，with a obviously increase in the content of acetic acid，propionic acid，butyric acid，and isovaleric acid （P<0.05， P<0.01） and the expression levels of HMGB1，RAGE，Toll-like receptor 2（TLR2），Toll-like receptor 4（TLR4），tumor necrosis factor-α（TNF-α），and nuclear factor kappa-B p65（NF-κB p65） proteins in cecal tissue were significantly decreased （P<0.05， P<0.01） in low-dose group of modified Sini San. Meanwhile，the contents of ZO-1，Occludin，and Claudin-1 in the cecal tissue were obviously increased （P<0.01） in low-dose group of modified Sini San. ConclusionModified Sini San can improve the function of intestinal mucosal barrier in chronic stress rats by increasing the content of SCFAs in the intestine and inhibiting the HMGB1/RAGE pathway.