Abstract: Objective To identify the pathogen and infection source of a food poisoning outbreak in a school and provide evidence for control measures. Methods Case survey, descriptive epidemiological analysis and case control study were conducted. Clinical samples from the cases and food processing people and food/water samples were collected for laboratory detection. Results The attack rate of food poisoning was 5.01%, and the cases occurred in 85.45% of classes in the school. The case control study indicated that the difference in OR of eating cold dish (OR=2.64,95% CI: 1.81-3.85, POR=0.37, 95% CI: 0.25-0.56, PSalmonella typhimurium were detected in the rectal swabs of 4 cases, which shared 90% homology and were classified as Ribo Group PVUII 515-6-S-1. Conclusion S. typhimurium contaminated cold dish was responsible for this food poisoning outbreak. No case occurred after taking appropriate measures.