Abstract： Objective:To observe the clinical efficacy of hyperbaric oxygen（HBO）combined with infliximab in the treatment of ulcerative colitis and explore its possible action mechanism.Methods:A total of 50 patients with ulcerative colitis were randomly divided into treatment group（26 cases）and control group（24 cases）. The treatment group was given HBO combined with infliximab，while the control group was given infliximab alone. Both groups were treated for 30 weeks.Results:The comprehensive efficacy，infliximab response rate，and trough level of the maintenance period（from the 3rd to the 5th injection）in the treatment group were significantly higher than those of the control group with statistically significant differences，respectively［92.3% vs. 66.7%， P<0.05；92.3% vs. 66.7%， P<0.01；（1.32±0.26）μg/ml vs.（0.74±0.22）μg/ml， P<0.01］；and the treatment group could significantly improve the levels of CD4 + and CD4 +/CD8 +，reduce the levels of CD8 +，TNF-α，IL-6，and CRP（ P<0.05）. Conclusion:HBO combined with infliximab in the treatment of ulcerative colitis can significantly improve the response rate of infliximab and enhance the curative effect，which may be achieved by inhibiting the proliferation of T lymphocyte and reducing the release of inflammatory factors.