ObjectiveTo explore the effects of Wumeisan on gut lactase activity and microflora diversity of mice with dysbacteriosis diarrhea. MethodThe mice were randomly divided into 4 groups， namely， the normal group， the model group， and the low-dose and high-dose Wumeisan groups， with 8 mice in each group. The mouse model was made by gavage of mixed antibiotics for 7 d， and the low-dose and high-dose Wumeisan groups （5.98， 11.96 g·kg^-1） were given gavage for 7 d continuously. The normal group and the model group were given the same volume of sterile water. The changes in the body weight， food intake， and diarrhea of mice were recorded. Feces were collected after the last administration， and the lactase activity was detected by the colorimetric method. The gut microbiota changes were detected by the 16S rRNA high-throughput sequencing technology. ResultCompared with those in the normal group， the mice in the model group had dilute and soft stools， reduced body mass， reduced food intake， reduced lactase activity， significantly reduced intestinal flora diversity， and significant changes in the relative abundance phylum and genus levels of flora. Compared with the model group， Wumeisan reduced the diarrhea rate of mice， promoted the rapid recovery of body weight and food intake， increased the lactase activity decreased by antibiotic， improved the community abundance and diversity of mice with dysbacteriosis， and made the species composition closer to that in the normal group. The abundance of three phyla （Bacteroidota， Proteobacteria， Verrucomicrobiota） and nine genera （Odoribacter， Enterococcus， Clostridium innocuum group， etc.） of mice with diarrhea were regulated by Wumeisan. Among them， norank f Muribaculaceae， norank f norank o Clostridia UCG-014， Lachnospiraceae NK4A136 group， and Odoribacter showed significant positive correlation with the body weight and lactase activity， and Escherichia-Shigella， Enterobacter， Enterococcus， and Clostridium innocuum group showed significant positive correlation with the diarrhea rate. Function prediction showed that the high-dose Wumeisan significantly reseted 6 functional levels of metabolism， genetic information processing， and human diseases， and had positive effects on endocrine and metabolic diseases， immune diseases， infectious disease， and parasitic infectious diseases. ConclusionWumeisan can relieve the symptoms of dysbacteriological diarrhea by increasing the lactase activity and regulating the gut microbiota composition.