Objective To explore the possible mechanism of Huayu Tongyang Formula（化瘀通阳方） in the treatment of ulcerative colitis（UC）. Methods A total of 24 Wistar rats were randomly divided into a blank group of 8 rats and a model replication group of 16 rats. In the model replication group

5% dextran sodium sulfate（DSS） solution was used to induce UC rat model. The 10 successfully modeling rats were randomly divided into a Huayu Tongyang group and a model group

with 5 rats in each group. The Huayu Tongyang group was given a retention enema with concentration of 0.54 g/ml Huayu Tongyang Formula at a dose of 2 ml

and rats in the blank group and model group received the same amount of normal saline enema for 10 consecutive days. After the intervention

the colonic histopathology was observed

and rat feces were collected for metagenomic sequencing analysis of intestinal flora. Results The colonic mucosa congestion and endema

structural disorder

and inflammatory cell infiltration in the submucosa were found in the model group; the structure of the colonic mucosa of rats in the Huayu Tongyang group returned to normal

with individual inflammatory cell infiltration and active gland hyperplasia. Compared with the blank group

the colon tissue injury index（TDI） score of the model group increased

and the genus and species levels of Prevotella decreased（P<0.01）. Compared with the model group

the rat colonic TDI score in the Huayu Tongyang group decreased

the genus level of Prevotella and the species level of Lactobacillus murine increased

the degradation of phenylalanine decreased

and the biosynthesis of lysine increased（P<0.05 or P<0.01）. Lefse ana-lysis showed that the differential bacteria in the model group were Clostridium

Turicibacter

and Faecalibaculum

and the differential bacteria in the Huayu Tongyang group were mainly Lactobacillus and Akkermansia. Conclusion Huayu Tongyang Formula can promote the mucosa healing of UC and regulate the abundance change of intestinal flora

and its mechanism may be related to the enrichment of Lactobacillus and Akkermansia.