Objective To analyze the effects of bifidum on intestinal flora and related immune function markers in patients with sepsis caused by lung infection， and to provide data for supporting clinical application. Methods One hundred and forty-three cases of sepsis caused by lung infection were randomly divided into two groups， including 71 cases of control group （received conventional treatment） and 72 cases of study group （received bifidum in addition to conventional treatment）. Critical illness scores ［Acute Physiological and Chronic health （APACHEⅡ） score and Sequential Organ failure （SOFA） score］ were evaluated before treatment and at 7 days after treatment， respectively. Fecal samples were collected to analyze the colonies of Lactobacillus， bifidum， Enterobacter， enterococcus， Escherichia coli and Clostridium. Peripheral blood was collected and the level of T lymphocyte subpopulation in blood was determined by flow cytometry. The plasma D-lactic acid and bacterial endotoxin levels were detected by intestinal barrier function biochemical index analysis system. The plasma levels of procalcitonin （PCT）， hypersensitive C-reactive protein （hs-CRP） and interleukin-6 （IL-6） were also determined by ELISA. Results Before treatment， there were no significant differences in critical disease score， intestinal flora number， intestinal function， T lymphocyte subsets and inflammatory factors between the two groups （P > 0.05）. After treatment， APACHEⅡ and SOFA scores in both groups were significantly reduced， and APACHEⅡ scores in the study group were significantly lower than those in the control group （P < 0.05）. After treatment， the number of Lactobacillus， bifidum and CD3⁺T% levels in both groups increased， while the number of enterococcus， Escherichia coli， intestinal function score， D-lactic acid， endotoxin， TNF-ɑ， IL-6 and IL-1β levels decreased. The levels of Lactobacillus， bifidum and CD3⁺T% in the study group were higher than those in the control group， while the levels of Escherichia coli， D-lactic acid， endotoxin， hs-CRP and IL-6 in the study group were lower than those in the control group （P < 0.05）. Conclusion Adding bifidum in the clinical treatment of sepsis caused by lung infection can improve the distribution of intestinal flora to a certain extent and alleviate the damage of intestinal barrier function caused by inflammation， which may be helpful to promote the repair of patients.