On March 19^th, many people hospitalized after lunch from a canteen of construction site in Shunyi District with symptoms of stomach burning sensation, nausea, vomiting and others. To find out the cause of disease development, control and reduce the disease harm. The emergency response unit of local CDC carried out epidemiological investigation.Methods Descriptive epidemiology, food hygiene survey and laboratory inspection was used to find out the cause, and traceability survey was also conducted. Results Investigation showed that the patients' clinical symptoms were mainly nausea, vomiting, dizziness, stomach burning sensation and the incubation period was 18 minutes, which was consistent with the characteristics of chemicals poisoning. The lunch meal was suspicious and the chefs used white powdery substance as salt to cook the first 5 dishes. Chemical composition of the substance was identified as magnesium silicofluoride and it was the major cause of poisoning.Conclusion The reason of 32 people poisoning was due to misuse of industrial chemicals by the chefs.