Objective To provide data support for infectious mechanism and microecological intervention strategies， the structural and functional alterations of the gut microbiota in patients with norovirus associated diarrhea was investigated and the potential microbial biomarkers was screened.Methods Microbiota structure and expression from fecal samples from 55 in 2018 norovirus-infected patients and 15 healthy controls were subjected to metatranscriptomic sequencing. Microbial community differences were assessed using principal coordinate analysis and non-metric multidimensional scaling. Differential taxa were identified by LEfSe and Wilcoxon rank-sum test， and a random forest model was constructed to screen for potential diagnostic microbial biomarkers.Results Norovirus infection significantly altered gut microbial composition and expression profiles. Enriched taxa in the infection group included Bacteroidota， Bacillota， Actinomycetota at the phylum level and Faecalibacterium， Bacteroides， Alistipes at the genus level. A random forest model based on genus-level abundances identified seven key genera with strong predictive performance （AUC=0.88）.Conclusion Metatranscriptomic analysis revealed that norovirus infection induces notable shifts in gut microbiota structure and function. Several enriched genera may serve as potential microbial biomarkers for norovirus infection， offering insights into microecological diagnostics and intervention strategies.