Objective To analyze anthe outbreak of norovirus infectious diarrhea in a school in Anqing City, and to explore the transmission routes and risk factors of the outbreak, so as to provide reference for the prevention and control of school infectious diseases. Methods Epidemiological investigation and school hygiene investigation were conducted with epidemiological questionnaires, and case-control investigation was carried out to understand the eating situation of patients.Cases were collected and norovirus nucleic acid was detected by fluorescence quantitative RT-PCR. Results The outbreak of norovirus infectious diarrhea in a junior high school in Anqing City affected 18 classes of 3 grades, with a cumulative incidence of 56 cases.The morbidity rate was 2.93%.Male students accounted for 3.94%, female students accounted for 2.21%3.94% for boys and 2.21% for girls.There was a statistically significant difference in the morbidity rate between males and females (χ²=4.443,P＜0.05).Classes with outbreaks were clustered.The incidence rate of norovirus infectious diarrhea was clustered in classes, and in public places of schools.Toilets and stairs in school public places may increase students' exposure risk.Anal swab specimens from 5 patients were positive for Norovirus GII nucleic acid.The toilets and stairs in 5 patients were positive for norovirus GII nucleic acid. Conclusion The epidemic was caused by Norovirus GII infection and transmitted from person to person.Aerosol transmission was not excluded.