Background and Aims Severe acute pancreatitis (SAP) is always associated with intestinal immune barrier dysfunction. The authors previously found that Huoxueqingjie (HXQJD) decoction can alleviate SAP damage, but whether this action is involved in the intestinal immune barrier function is unclear. Therefore, this study was conducted to investigate the effect of HXQJD decoction on the intestinal immune barrier function in rats with SAP, and the mechanism.Methods The SD rats were randomly divided into sham operation group, SAP model group (SAP group), and SAP model plus HXQJD decoction treatment group (treatment group). The SAP model was established by retrograde biliopancreatic duct infusion of 5% sodium taurocholate (NaT). After the operation, HXQJD decoction was administrated by gavage in the treatment group, and the sham operation group and model group were treated with normal saline in the same fashion. Rats were sacrificed at 6 and 12 h after the operation. The serum pro-inflammatory factor TNF-α, anti-inflammatory factor IL-4, as well as blood amylase and lipase levels were detected by ELISA assay. The pathological changes in the pancreas and small intestine were observed by HE staining. The expressions of M1 macrophage phenotype marker iNOS and M2 macrophage phenotype marker Arg-1 in small intestine tissue were determined by qRT-PCR and Western blot. Rat intestinal macrophages were treated with NaT, HXQJD decoction, or NaT plus HXQJD decoction, respectively, using the untreated rat intestinal macrophages as blank control. The expressions of NF-κB, iNOS, TNF-α, Arg-1, IL-4, TIPE2, and PPAR-γ were examined by qRT-PCR and Western blot, respectively.Results In invivo study, the levels of TNF-α, IL-4, and serum amylase and lipase were increased in different degrees after operation in model group and treatment group compared with sham operation group (partial P<0.05), but the increasing amplitudes of TNF-α, and serum amylase and lipase were lower while increasing amplitude of IL-4 was greater in treatment group than those in model group (all P<0.05); evident pathological injuries were seen in the pancreas and small bowel in both model group and treatment group, but the degrees of injuries were milder in treatment group than those in model group, the injuries were worsened in model group while were alleviated in treatment group with the prolongation of time, and the pathological scores for pancreatic and intestinal tissues were significantly different between model group and treatment group (all P<0.05); the protein and mRNA expression levels of iNOS in the small intestinal tissue were significantly increased in model group while were significantly decreased in treatment group (all P<0.05), and the protein and mRNA expression levels of Arg-1 were significantly increased in late stage in model group while were significantly increased in both early and late stages in treatment group with greater increasing amplitudes than those in model group (all P<0.05). In invitro study, the protein and mRNA expression levels of NF-κB, iNOS, and TNF-α were significantly increased (all P<0.05) while Arg-1, IL-4, TIPE2, and PPAR-γ showed no significant changes (all P>0.05) in the rat intestinal macrophages after NaT treatment alone; the protein and mRNA expression levels of Arg-1, IL-4, TIPE2, and PPAR-γ were significantly increased (all P<0.05) while NF-κB, iNOS, and TNF-α showed no significant changes (all P<0.05) in the rat intestinal macrophages after HXQJD decoction treatment alone; the protein and mRNA expression levels of NF-κB, iNOS, and TNF-α were significantly decreased while Arg-1, IL-4, TIPE2, and PPAR-γ were significantly increased in rat intestinal macrophages after NaT plus HXQJD decoction treatment compared with those after NaT treatment alone (all P<0.05).Conclusion HXQJD decoction offers a protective effect on the intestinal immune barrier function in SAP rats, and its action mechanism may be associated with it regulating the transformation of intestinal macrophages from M1 type to M2 type, promoting the expression of anti-inflammatory factors and inhibiting the release of pro-inflammatory factors, thereby alleviating the systemic inflammatory response.