Objective： To observe the effect of Huanglian Jiedu Decoction on intestinal flora in patients of anal fistula with dampness-heat diffused downward type by the technique of 16S rDNA high-throughput sequencing.,Methods,2,A total of 40 patients of anal fistula with dampness-heat diffused downward type were included and randomly divided into the traditional Chinese medicine group and control group， 20 cases in each group. The patients in both groups were treated with ligation of intersphincteric fistula tract （LIFT）， and the patients in the traditional Chinese medicine group were orally treated with Huanglian Jiedu Decoction before operation for 2 weeks. One day before operation， the serum and fecal samples were collected. The levels of serum interleukin （IL）-1β， IL-2， IL-4， IL-5， IL-6， IL-8， IL-10， IL-12p70， IL-17， tumor necrosis factor-α （TNF-α）， interferon （IFN）-γ and IFN-α were detected by ELISA. The composition characteristics of fecal intestinal flora in both groups were detected by 16S rDNA high-throughput sequencing. Twelve weeks after operation， the clinical effect was evaluated.,Results,2,The levels of IL-8， IFN-γ and IFN-α in the traditional Chinese medicine group were lower than those in the control group （,P,<,0.05）， and the clinical efficacy of the traditional Chinese medicine group was significantly better than that of the control group （,P,<,0.05）. The results of 16S rDNA high-throughput sequencing and biochemical analysis showed that there were significant differences in the intestinal microbiota between the two groups. On the level of Phylum， the Actinobacteriota and Cyanobacteria Phylums were mainly enriched in the traditional Chinese medicine group （,P,<,0.05）， while the Fusobacteriota Phylum was mainly enriched in the control group （,P,<,0.05）. The results of functional enrichment analysis showed that the bacterial nucleoid DNA-binding protein and outer membrane receptor for ferrienterochelin and colicins were enriched in the traditional Chinese medicine group （,P,<,0.05）. The results of pathway prediction showed that the metabolic pathways such as peptidoglycan biosynthesis and cytochrome c were enriched in control group （,P,<,0.05）.,Conclusion,2,The anti-bacterial and anti-inflammatory effects of Huanglian Jiedu Decoction may be through improving the intestinal flora in patients of anal fistula， reducing the relative abundance of harmful bacteria and enhancing the relative abundance of beneficial bacteria， and may have relationship with increasing the expression of bacterial nucleoid DNA-binding protein， increasing the expression of outer membrane receptor for ferrienterochelin and colicins， and inhibiting the metabolic pathways such as peptidoglycan biosynthesis and cytochrome c. Therefore， this formula can be used as a preoperative adjuvant treatment for patients of anal fistula， or as an alternative for conservative treatment and being unable to operate in time.