Objective To survey the cause of an outbreak of infectious diarrhea in 7 middle schools in Tangxi township of Yuhang country, and take control measures. Methods Questionnaire survey and case-control study were conducted, the data were analyzed statistically by using SPSS 13.0. The anal swabs, throat swabs and vomits were taken to detect norovirus by PCR. Results Thirty two samples were detected to be norovirus positive. The positive correlation was observed between the disease onset and the amount of barrelled water drinking (r=0.900,P=0.037), the negative correlation was found between the disease onset and the frequency of washing hands before eating and after defecating(r=－1.000,P=0.000), and Roommates or close contacts of the cases were found to be associated with the disease statistically . Consicluon The contamination of barrelled water by norovirus type I was the infectious source of the disease, meanwhile there were other transmission routes which included close contacting with the patients and the spread of aerosols formed from the patients vomits and feces.