ObjectiveTo evaluate the clinical efficacy of modified Banxia Xiexintang combined with vedolizumab （VDZ） in the treatment of active moderate to severe Crohn's disease （CD） with the syndrome of cold and heat in complexity and the effect of the therapy on intestinal flora. MethodEighty patients were randomized based on the random number table method into a control group （40 cases） and an observation group （40 cases）. The control group was treated with VDZ， and the observation group was treated with modified Banxia Xiexintang （1 bag per day） combined with VDZ. The treatment in both groups lasted for 14 weeks and the follow-up lasted until the 52th weeks. The CD activity index （CDAI）， CD simplified endoscopic score （SES-CD）， inflammatory bowel disease questionnaire （IBDQ） score， and syndrome score of cold and heat in complexity were assessed before treatment， after treatment， and at the end of follow-up. The levels of hemoglobin （HGB）， hematocrit （HCT）， albumin （ALB）， C-reactive protein （CRP）， interleukin-6 （IL-6）， tumor necrosis factor-α （TNF-α）， interleukin-17 （IL-17）， and fecal calprotectin （FC） were measured before and after treatment. Intestinal flora was examined before and after treatment. The safety of the therapy was evaluated. ResultCompared with those before treatment， the scores of CDAI， SES-CD， and the syndrome of cold and heat in complexity decreased （P<0.05） and the IBDQ score increased after treatment （P<0.05）. Compared with those before treatment， the scores of CDAI， SES-CD， and the syndrome of cold and heat in complexity increased （P<0.05） and the IBDQ score decreased （P<0.05） at the end of follow-up. After treatment and at the end of follow-up， the observation group had lower scores of CDAI， SES-CD， and syndrome of cold and heat （P<0.05） and higher IBDQ score （P<0.05） than the control group. Moreover， the observation group had higher clinical remission rate（χ²=4.381，3.962） and response rate（χ²=5.541，4.306） and lower non-response rate（χ²=6.646，4.306） than the control group at the two time points （P<0.05）. The endoscopic remission rate（χ²=4.072，3.985） and response rate（χ²=4.528，5.161） in the observation group were higher than those in the control group （P<0.05）. After treatment， the HGB， HCT， and ALB levels in both groups elevated， and the observation group had higher levels than the control group （P<0.05）. The treatment in both groups lowered the levels of CRP， IL-6， TNF-α， IL-17， and FC （P<0.05）， and the observation group had lower levels of CRP， IL-6， TNF-α， IL-17， and FC than the control group after treatment （P<0.05）. The relative abundance of Bifidobacterium， Lactobacillus， and Prevotella increased （P<0.05）， while that of Proteus， Klebsiella， and Enterococcus decreased （P<0.05） in the two groups after treatment. Moreover， the changes in the relative abundance of these bacteria in the observation group were more obvious than those in the control group （P<0.05）. No adverse reactions related to the modified Modified Banxia Xiexintang were observed during the study period. ConclusionModified Banxia Xiexintang combined with VDZ can play a synergistic role and has good short-term and long-term efficacy. This therapy can improve the nutritional status， regulate intestinal flora， and reduce inflammatory injury in the treatment of moderate to severe active CD patients with the syndrome of cold and heat in complexity without causing severe adverse reactions.